Online backup systems like Carbonite and MozyPro do a great job of protecting your data from a catastrophic loss, but that's about all they're good for. They don't take advantage of the collaborative nature of the Internet and aren't especially useful for day-to-day document management and file sharing.
Full-blown online document-management systems, on the other hand, offer lots of features that backup-only services don't - but they can be complicated to set up and learn, and have more functions than many of us will ever need.
A third type of web-based file-hosting service has the potential to completely change how you use computer technology. Like backup-only, these "save-and-sync" services keep your data secure and backed up "in the cloud," where you can access it from a web browser. In addition, many of them can place a copy of whatever is shared online onto other computers or mobile devices "on the ground," which means you can work on those files without always having to be online.
So What?
Storing your files and folders in the cloud means that as long as you have Internet access, you can get to them. Say you're at a supply house and you need to quickly view a project's specs. No problem - you can do it from your mobile phone. If you're at a customer's house and want to discuss the latest CAD revisions, you can access the drawings from your laptop. If you've got a PDF product catalog that's too large to email, you can share it in the cloud and let the other folks open a copy on their own computers.
Then there's disaster recovery. I recently had not one but two laptops blow up on me in one month. Since all my data was in the cloud, it was a minor inconvenience instead of a business-ruining catastrophe.
Services that share copies of files locally make it easy to selectively share information with other users - the files just magically show up on their computers. You don't have to struggle with emailing large files, and the other people involved don't have to learn anything new or log into something online. Best of all, when a file is changed, everyone connected to that folder gets an update, so everyone is always working with the most current copy.
You can use that feature to set up a folder for each job you're doing, and then share a particular job folder with only the customers and subs associated with that job. Likewise, you can set up a financial folder that you share only with your accountant, or a folder with house plans you're developing that you share initially with your draftsman, then later with suppliers so they can access the drawings and upload their quotes. All of this can happen without the hassle of emailing files back and forth or the risk that somebody will use an outdated version of the plans (or that you'll work from an old quote).
Some Available Services
Below I've reviewed six of the most popular save-and-sync services, but there are new services popping up all the time. All the ones I've included will store files on the web and synchronize them with other computers, and most have dedicated client software available for mobile devices like smartphones and tablets. Now that most mobile devices will let you at least view (if not edit) common file types, these services can help you replace an office trailer full of filing cabinets with your shirt pocket!
One caution: Most of these save-and sync services use much simpler access control and sharing permissions than you'll find in full-blown document-management systems like Microsoft SharePoint. You're not likely to find role-based access control (where customers and subs get different files in a folder) or check-in/check-out, which locks documents in use to prevent them from being edited by others. For most of us, though, these limitations won't be a big deal.
Dropbox. Founded in 2007, this was one of the first save-and-sync services, and it's still the standard by which others are judged. Dropbox allows you to invite people by email to join your password-protected folder. Once they do, a copy of the folder and its contents is created on their computer or mobile device. Changes are automatically synchronized through the system so that the original file, the version stored in the cloud, and all the locally shared copies are always up-to-date.
Dropbox synchronizes everything in its cloud by default. However, you can disable synchronization of any folder - to conserve space on your local hard drive, say, or so that you can use Dropbox for archival storage of files you want backed up but don't need to work with day to day.
One feature can take you by surprise: People you invite to your folders can delete files, and when they do, the files disappear from everywhere - including your hard drive. Luckily, Dropbox stores six prior versions for 30 days. If you plan on sharing a lot of files, consider Dropbox's optional $4 per month "Pack-Rat" add-on, which makes every file recoverable (supposedly) forever. Dropbox also has a "Teams" plan that costs $795 per year for up to five users and $125 for each additional user. It offers unlimited storage and includes the Pack-Rat feature.
Box. This service has morphed from a simple "hard drive in the sky" to a complete business collaboration system - with a few catches. To get the full monty of features - such as role-based access permissions and the ability for collaborators to have local copies of files instead of just accessing them online - you need a business account, which provides a terabyte (1,000 GB) of online storage with a three-user minimum. Box also offers personal accounts, both free and paid, but you have to sign a "not for commercial use" agreement.
Box has client software for smartphones and tablets, and its business edition goes a step further by bridging the online-offline world with a variety of "partner" applications that make your Box files and folders available directly in desktop applications like Microsoft Office and cloud apps like Google Docs. Box Business also has an integrated project-management system that lets teams assign and track tasks around document creation and collaboration.
SugarSync. Of all the services described in this article, SugarSync probably has the widest range of features. In addition to the usual mobile platforms, it has native client software for Windows Mobile and Symbian phones. Outlook users can download an add-in that allows them to email files into their "personal storage cloud."
CrashPlan. This open-source alternative calls itself a "backup" service (more akin to Carbonite or MozyPro), but because it also syncs files between multiple PCs and its own cloud service, I'm including it here. CrashPlan has both consumer and pro plans. The consumer plans are cheap - $5 per month for unlimited online storage and $12 per month for up to 10 computers in the "family plan."
A nice twist is you can use CrashPlan for free to sync as much data as you want between your own computers; you pay only if you use CrashPlan's web storage. That makes it a good choice for someone who works with files that are too large for practical online backup - like high-resolution photos or videos - and wants an easy way to back them up on multiple computers, maybe between a computer in the office and another one at home. Though not as convenient or stable as a data-center backup, this approach is definitely better than doing nothing, and CrashPlan's tools can make it happen automatically in the background.
Syncplicity. Like Box, Syncplicity - a relative newcomer - uses partner applications to extend the reach of its services across a broad range of platforms and business applications. It has personal accounts, but the good stuff requires a business account, which starts at $45 per month. Syncplicity business plans integrate with Google Docs, Microsoft SharePoint, Salesforce.com, and other common cloud-based applications.
Ubuntu One. This is another open-source service. Developed on the Ubuntu Linux platform, it's the only option in this roundup that doesn't have a native MacOS client (though it does have an iOS client for iPhones/iPads). Where Box and Syncplicity are all business, Ubuntu One was built for personal use. You won't find integration with Google Docs or Microsoft SharePoint, but you can install an add-in to stream music from your Ubuntu One account to any of your devices.

What Works For Me
I've used every one of the contenders listed here, as well as some I didn't include. Dropbox has proved to be the best fit for my business. Previously I was using an online backup-only service along with a hodgepodge of online file-management and collaboration systems, each with its own log-in and quirks to remember. Since Dropbox effectively provides the same file security as the backup-only services - and since its file-sharing capability is adequate for what I need to do - I decided to simplify things and use it alone. I opted for 100 GB storage.
This change involved moving all my files, so I made sure I had two complete backups of everything before I started, as insurance against the remote chance that a glitch in the process could cause data to be lost. I did one backup to my MozyPro account and another on a local USB hard drive.
Dropbox sets up a folder on your hard drive called "Dropbox" or "My Dropbox" (depending on your version of Windows). The default location is inside the Documents folder, but you can have it placed wherever you want. I put mine at the same level as Documents in the root of my Windows User Profile. Next, I moved (rather than copied) all my subfolders and files from Documents into the Dropbox folder. This is an easy Windows Explorer operation that can be done with keyboard commands or with your mouse.
While the files and folders in the main Dropbox folder were synchronizing with Dropbox on the web (an operation that took a couple of days), I tweaked every one of my software applications to use "Dropbox\" as its default "save to" location. I also scoured my hard drive for other files I wanted to be backed up automatically, and modified those locations to use the Dropbox. It's amazing how much critical data is saved by Windows outside of Documents: your Outlook .pst file, the QuickBooks "company" file, custom dictionaries and signatures in Outlook, Microsoft Office templates, configuration and .ini files, and libraries of CAD symbols, textures, and components.
Practically every application I use has some custom configuration, so this part of the process took some work. But it was definitely worth the effort, because I no longer have to worry about manually backing up those files.
JLC contributing editor Joe Stoddard moderates the Business Technology forum at jlconline.com.