0.001% is still probably a generous estimate -- given Facebook's 3000 or so employees and the fact that all not-very-senior employees should add up to 2%.

Also, stock options need to have a hardly-discounted exercise price attached. That is, an employee that gets a stock option package reflecting shares worth $500K will have to shell out (at least) $450K to exercise them when the time comes. So based on this valuation, if facebook is worth "only" $70B in 4 years, the profit is going to be $250K or ~$60K/year. Nothing to sneeze at, and definitely a nice bonus -- but not more than that. And if facebook is worth $30B at the end of 4 years, today's stock option grant is worth virtually nothing.