As of this morning (or at least sometime before lunch), Zoho Writer turned on offline mode with Google Gears. If you haven't heard about Gears yet is a small application (and framework for developers) to enable Ajax applications to go offline. It uses a very small local server and database to grab all the data you would need should the application go offline (this has to be set up by the developers of the application). There is a great podcast about it [here](http://google-code- updates.blogspot.com/2007/06/google-developer-podcast-episode-three.html) from the Google Developer Podcast. The first Google product to use it was Google Reader which I though was pretty nifty. Before you go on a trip, just hit "Go Offline" and it will download all of your unread posts... get on the plane and shazam, all your reading to keep you busy.
Zoho currently only supports offline read which I assume means Gears will grab all of your documents and you can read them over. Zoho says they will be adding read/write functionality in 3-4 weeks.
I must say though, I'm very disappointed that Google got beat to having this in Docs and Spreadsheets first. I'm sure it would help a great deal with the Google Office Hacks book that Philipp Lenssen is writing. C'mon Google, GET IN GEAR(S)!!