I was able to try Google Docs Offline for the first time today and it's extremely cool.
The offline function uses the Google Gears web browser plugin which I talked about last June to keep an offline copy of all your documents. If you find yourself outside "the cloud" with no Internet access you simply point your web browser at the docs.google.com domain and your browser reverts to the offline version. You can view documents and spreadhseets and even edit your documents offline and it automatically syncs your changes when your conection is re-established.
It was a tiny bit buggy for me when I first used it, but I think this is a significant step forward for web applications. I really hope that open standards emerge so that this kind of thing becomes commonplace, there are certainly efforts to make this happen.