Indeed, Facebook could provide a collaboration model for the future. I don't think the collaboration platform will be Facebook itself (not their focus) but perhaps a startup will come along, look at how people communicate on Facebook, and apply that to business. Wait - there are guys doing that now (I love how framing something by typing it out fleshes out your thought process!) I saw a good presentation on HN on Enterprise 2.0 recently, I'll try and find the link.
EDIT: Jive are one example, not the link I had in mind though: