While Google Wave developers are polishing their product for launch Etherpad have slipped in with one bit that will certainly cause quite a stir - the document screen where you and others can interact in real time. It's quite an odd experience at first, watching someone else move your text around and add theirs - but you'll get used to that soon enough and appreciate the benefits and advantages.
This is certainly worth experimenting with - public spaces are free but if you want to work privately with a title.etherpad.com address to store work the free version is limited to 3 colleagues. I'm a bit surprised at the $8 a month fee for more people at this early stage. Few people will have heard of this and are unlikely just to buy, however cool the instant participation is. And, of course, Wave's on its way, and that will be free and, I rather suspect, knock anything like this into the wilderness.