The money that was there to be made in the Facebook IPO was made before Facebook went public in the secondary market. For professional investors that are getting in at the seed round until the C round or so, Facebook isn't indicative of a problem. Those investors can still make money, it's just that they are going to exit via secondary markets now instead of an IPO.
Will Facebook get back to $100b and beyond? yes as soon as it starts making more money.
Some people (including me) just think the E is going to move up, rather than the P move down. I made this mistake with LNKD -- thinking it was an absurd P/E, not realizing that the costs were relatively constant and that increasing revenue would produce huge increases in profits.