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.
Google Wave was just a fancy message board system anyway. As much as they were raising hype about it being new and exciting technology, it really wasn't.
I thought the tech behind google wave was pretty cool.
I found some php/javescript code online for a google wave like comment system with live updating and playback, I was thinking about adding it to my website just for coolness factor
besides being cool for a web app I also agree that it was useless.
As for facebook, it seems like a female ego parade to me, but that might be because I have the wrong friends.