It's a popular request from people that want to access/edit their Google Docs even they are offline. Just like having the file in the hard drive and modify. Now it's possible with the help of Google Gears. Google just announces it rolling the new functionality to everyone. Here is a video from Google to demonstrate Google Docs offline.
Right now, it only works on word processing documents, (no spreadsheets or presentations support yet.) but I think it's just a matter of time that it will be available on spreadsheets and presentations.
Update: Google Docs offline works for my account now. 4/22/2008