For a group projects (hardware and software) Google wave was very handy and useful, but that is kind of a niche area and we still use my server mainly anyway (for project folders). We mainly used it for brainstorming and generating ideas/doing little sketches/pseudo code in real time.
@OMC: I shall not comment on my views on Facebook already made them apparent on here elsewhere
I thought the most promising part about Wave was the possibility of writing code at the same time with other people. There wasjust too much lag involved to make it viable, though. Easier to do code branching, I'm told.