Portable writing alternatives

Lately, I've been finding myself away from home and with the time to write. I don't have a laptop, so that sort of portability is out for me and I'm looking at other alternatives.

Probably the most obvious choice is GoogleDocs (http://docs.google.com), or a similar web-based word processor. My question is - is anyone else out there using GoogleDocs, or another web-based processor? And, how successful (or unsuccessful) has that been for you?