There's already billions of shares out there, and a clear resistance to selling shares under $20.
Insiders are going to think long and hard about selling shares under $18 when the potential upside in just a few months is huge.
I think we all know that these FB insiders are not going to give up the chance to make a killing, by selling a stock at $10 that could be $100 in a few years.
They are saying to themselves, ok the IPO was botched, but look at the way the market is valuing LNKD now. I'll sell a third of my shares now, and a third in 2013, just to make sure I don't miss a big move upwards.
Since the big dump of shares isn't until after the next time FB reports earnings - or who knows what other new monetization schemes - buying at an $18 floor now in August, while indeed a risk, could end up as the smartest move any investor ever makes.