With Zuckerberg pledging not to sell a single one of his shares during the next year (http://goo.gl/XkPk1) maybe some of Facebook's employees will be convinced to do the same?
I highly doubt that. Zuckerberg would have cashed out a ton in the lead up to the IPO already (he at the very least took a 1M bonus years ago and took a pretty hefty salary before the IPO), but many senior people probably don't have millions of dollars in cash in the bank ...