They claim 500MM active users. Assume that's a total lie, and it's 50MM. Assume their valuation is 100 billion (twice the Goldman round).

Let's also assume that they hit a P/E ratio of, oh, 10. (Google's at 22, Apple 19, Yahoo 18, so 10 is really low.)

So to hit a 100b valuation, they'd need to earn 10b annually, or $200/user.

$200/user is on the high end, but reasonable, at least as far as U.S. users are concerned.

(For what it's worth: Twitter would have been a good example, I think.)