Advertising itself as a cheaper Dropbox alternative with a better feature set, Insync has been in closed beta for the last 15 months. Now, they're finally ready to launch with a service that tightly integrates into Google Docs. It's "8x cheaper" than Dropbox, according to their marketing; in fact, the core service is now free, and customers who paid for the service during the beta period will be offered a refund or premium service credit. The only cost for basic membership is the cost of Google storage.
Insync brings a number of novel features to the table, differentiating it from Dropbox's current service. For example, you can share individual files with more granularity -- not just as public links, but specifying read-write or read-only permissions. You can also revoke a sharing link, which isn't possible on Dropbox unless you move or delete the shared file.
All your files live inside your Google Docs account, but that doesn't mean you're limited to the supported Google file types; any file can be synced over, as long as it's less than 10GB in size (assuming you have that much room in your storage allocation).
You can nest sharing privileges so people have access to just part of a folder structure. You can also set re-sharing permissions, specifying whether those you share with can re-share that material or not. Share recipients are not charged against their storage quota.
Insync supports multiple Google accounts and uses Google's storage system. Google starts with 1GB free storage, and then moves to 20GB for $5/year up to 16 TB for $4096/year. Dropbox's pricing rates includes 2GB free storage, and then jump to 50 GB paid storage at $10/month. Dropbox's 50 GB will cost you $120/year compared to Google's $20/year for 80 GB. That's $0.25 per GB per year for Google Docs versus $2 per GB per year for Dropbox.
To use Insync, you sign in with your Google credentials and permit it to gain access to Google Docs. You then download and install the client software on your computer. From there, you launch, link the Google account to your machine, and you're ready to go. On OS X, all your Google Docs appear in a Finder window.
In its current incarnation, Insync feels a lot like Dropbox, including its menu bar widget and small status indicators next to files (both Egnyte and Box.com use similar UI conventions for their respective cloud sync tools). If you're used to Dropbox, then you already know how to use Insync.