In my mind (and maybe I missed some aspect of the Facebook announcement) Wave was much more ambitious due to the collaborative document editing aspect, absolutely realtime interaction, and open architecture/apis that allowed for things such as bots and interaction from external systems.

It seems that Facebook's system has some of the same elements/ideas as Wave, but I wouldn't say it fills the same space as wave.

Exactly what I was thinking - it sounds interesting when viewed from that perspective..