In this case, I wouldn't care much about the growth of the user base, which is pretty ubiquitous regardless of some dropoff or slow growth. Rather, the only number I'd care about is the growth of profits and advertising, which is relatively unknown at the moment.
facebook should have been trading for a year already. and now the market is entering what could be a protracted decline. this reminds me of companies that went public in february of 2000. so obvious the train had already left the station...