Here's one I've done earlier for the medical library's 23 Things programme (don't you just love when they overlap?) We've also been using Google Docs in planning (lib)TeachMeet, as Katie and Celine have already mentioned. I find it handy for keeping a back-up of work-in-progress documents such as essays or for sharing content with others, but the formatting problems mean that I wouldn't bother working with it all the time.
demise of Google Wave. I did post a comment about this on Ange Fitzpatrick's post but it's not appearing yet. There, I agreed with those who say Wave's problem was the lack of purpose - it was fun to play with but it never made sense as a standalone product.
There is definitely scope for its functionality to be incorporated into Google Docs and also into GMail though, and I think this would make collaborative working online much easier for all of us.
[This image of a kayaker catching a wave comes courtesy of Tommy P World. Another blast from the past, not that I was ever the best paddler in the world...]