Most employees have a stock strike price that is say $2.00 when the company is valued at $20.00.
So if each Foursquare stock was worth $20 and is now worth $10, the strike price of $2 still allows employees to make $8 per share now.
If you are granted 100,000 shares and wait it out and build the company back up to $20 you will make $18 per share times 100,000 shares for a nice little $1.8M bonus for putting in the hard work.
Maybe because you stuck it out you not only increased the price to $50 per share, but you were also granted 100,00 more stock because you didn't care what TechCrunch said. $9.6M isn't bad for 4 years of hard work...