[it] will pull down all of your documents and spreadsheets from the service, making them available to read and access even when away from a data connection.
All you have to do to get any document cached for offline viewing is open it once. If there are any changes since the last time you accessed it, they'll be download the next time it syncs back up with Google's servers. If you're worried about privacy you can also completely clear out the cache whenever you please.
The big question hesitant users have about web-based applications like Gmail is: "How do I get my data if I'm offline?" A beta, open source project called GCalDaemon attempts to answer to this question.
Apple's Time Machine is a great feature in their OS, and Linux has almost all of the required technology already built in to recreate it. This is a simple GUI to make it easy to use.