Using Google's vast resources in ways that company did not intend is not a new thing, though rarely is it done right. A new service from the Philippines called Insync falls into that small category, while still managing to play by the rules.
Insync does one thing and does it well, which is to use your Google account as a storage locker. This in itself is not that big of a deal since Google has offered general file storage within Google Docs since January. What Insync does that's so special is turn that storage into a local folder you can access on your computer, just like you would any other folder. Any changes you make to this folder get synced back over and vice versa, and like competitor Dropbox, you can link it up to multiple machines.
One thing that's required for using the service is the installation of some local software, which works on both PCs and Macs, runs quietly in the background, and syncs over any changes. It also gives you a visual indication of when files are being transferred, or updated to a newer version.
In my testing the software worked well, though it wasn't quite as good as some other desktop sync apps like the aforementioned Dropbox or Sugarsync--both of which offer progress bars for how far along a large file is to transferring. Not seeing this for a 114MB video I uploaded meant this turned into a bit of a guessing game for when it would finish. The good news is that Insync's creators tell me such an indicator is on their road map.
Insync has a few other bells and whistles including revisioning, which lets you download variations of files; a rundown of file activity; and sharing, which works just like it does over on Google Docs.
While the service is software-centric, users can also download files through a Web interface, though you're unable to rename or reorganize them using it. These two shortcomings are being addressed in future versions of the service, however, you can make these kinds of changes over on Google Docs and they'll sync up. Another shortcoming worth mentioning is that you only get 1GB of storage through Google unless you've invested in one of the paid storage plans. If you're just using Insync on some PDFs, Microsoft Office documents, or another smattering of small files this isn't a big deal, but in the world of Web storage, 1GB can fill up quickly.
Google Apps users looking to add it to their accounts can find it in the Google Apps Marketplace.