For me, liquidity would be a concern. I don't think I would want to invest at FB at the currently quoted 25$ billion level if I had to leave my money there for a very long time; so much can change, and I share some concerns about the company's future, at least where valuation is concerned.

The question here though, is about an IPO. I think that the markets would eat up FB, but it's dicey to try to time such things -- have a look at Tesla, for example! -- and easy to be correspondingly burned. I presume that if we follow this question to its logical conclusion, assuming Facebook has an IPO sometime in 2011, I don't know I'd want to take a bite - I think it would get overvalued in the public markets, especially at first, and I am not sure about long-term growth. Huge potential, but can they execute? I would want more diversification, and I wouldn't want to buy a small enough chunk of FB to feel safe about that investment; wouldn't be much point. I would be happy to have it join a roster of other more broad tech investments of mine, though, all things considered.

Interesting to see the contortions FB has to make to stay under the 500 # to avoid publicly filing with the SEC ; )