Wave was a horrible implementation of a decent idea. For the longest time it felt like they did absolutely no work on the wave project (at least not from the users perspective).

I think the main problem with wave was that it wasn't solving any problems it was just mashing up a lot of features in to one application and never recovered from performance issues.

Google Wave was a great idea but making it standalone application was the mistake, IMO. I am pretty sure the ideas Google Wave generated will be implemented on the right application someday. Facebook might be the platform for Lars to implement his pet project (Wave).