After a long build-up, Sharpcast has unveiled its service SugarSync, which uses the online “cloud” to sync files across multiple computers and mobile devices.

We’ve been excited about the company for a while, because it looked to be creating the “killer app” that really, truly helps a mass audience access and manipulate their files remotely. That excitement, in part, is why we sounded a little underwhelmed in our coverage when SharpCast launched with only a photo service a year ago. But SugarSync looks to be the real deal: it automatically shares files in any folders that you’ve selected, and it also updates (syncs) those files as you change them.

SugarSync has been in development for four years, which means the service will now have to compete with other companies trying to do the same thing. The closest competitor may beDropBox, which came out of secret testing mode about a week ago ( our coverage). But SugarSync has a number of significant advantages, including compatibility with mobile devices and televisions, and the fact that it can sync any file on your computer (not just those in a specific folder or “dropbox”). After all, the more devices you can access your data from, and the less you have to change your behavior to get sync to work, the better.

This is also a field that the big tech players are also looking to enter. For example, Microsoft announced earlier this month that it’s trying to develop similar “mesh” technology. But Microsoft is still in development mode, whileSugarSync is a reality, notes chief executive Gibu Thomas. And since one of the big goals of sync is to link files across platforms and operating systems, it helps that SugarSync doesn’t have anything at stake the way Microsoft does.

“When you’re building bridges, you want to be Switzerland,” Thomas says, “I don’t have an fiefdoms to protect.”

So here’s how it works: after you install SugarSync, you select the folders that you want to be automatically synchronized. (If you don’t want your general Documents and Photos folders to be synced, you can also just use a new Magic Briefcase folder, which seems to function similarly toDropBox.) After that, SugarSync just runs in the background; if one of your SugarSync enabled devices is turned off or goes offline, it will automatically updated once you go online again. There’s also a “Light Sync” option, which allows you to keep abreast of updated files, but won’t actually download them to your computer or device until you want to.

On a journalist’s salary, I’ve only got one computer, so SugarSync is a little less useful for me, but by uploading all of my content onto the cloud — in other words, SugarSync’s server — I can now access all of those folders anywhere I can get onto the Internet.

Following this free trial period, SugarSync will be charging for monthly subscriptions. Thomas says he also hopes to strike licensing deals with carriers like AT&T and Verizon. Long-term, Thomas wants to releaseSugarSync’s APIs so that developers can build other applications around the company’s sync technology.