Google has put Writely up for users to try. Remember when you sign up that it is a beta and you're supposed to be hunting bugs.
I've used it. It works better than any previous version and I think it approaching the level of usefulness that will be demanded by most folks. You power users of word processors are going to wait for a while to get all the features you need.
If you don't mind a little bug documentation, this is a good thing to check out. It's also a fine demonstration of an AJAX web app and as such it really does fire up my imagination..