I would never invest in Facebook until they actually had a real profit model. The only product they have is marketing and advertising. That's fine, but it's not diversified. Give me a break..they need actual other products in case one thing hits the fan, they have backups.
Why don't they do Facebook for business? Internal social networks. There's already products out there that do that, but they are nowhere near as "good" as Facebook. Some people say Facebook Groups can do it? They can do much better. I guarantee most businesses want actual control of everything.
How about a pro user that offers people tools to increase their users and possibly revenue? I guarantee you if the price was right, companies would definitely pay for that. LinkedIn does a similar thing with the Pro User.
If FB tanks, I could see a company like Yahoo, Google, or Microsoft buying them. It will happen if it tanks.