There have been so many articles speculating on the true value of Facebook shares. The truth of the matter is that the market sets the value - and it's just adjusting Facebook's, and other people's expectations at the moment. $13.80 is pretty good value for a share - it gives plenty of space for bumps upwards in the market (key sales, acquisitions and appointments).
The only way to go after an IPO like Facebook's is down. Look at the way the UK market contracted after Lastminute.com's IPO. These are more mature digital times, but there are still lessons to be taken from it.