The Rasmussen brothers created an interesting product, but the lack of ease, lack of integration with existing products (both Google's & others), and Internet user behavior did not bode well for Wave.
I really, really liked the promise of being able to tie conversations across different platforms into one thread (e.g. email, blog, micro-blog, etc.), but, like others, I found the service difficult to incorporate and somewhat siloed.
Lessons:
1) Keep It Simple Stupid (KISS)
2) Demonstrate within 60 seconds how it will easily integrate into a user's habits
3) Demonstrate and make incremental steps to changing user behavior (or demonstrate the value of radical change in such a way that users can't resist adopting)
Here's Google's blog post on the matter.
