Are you planning making remote logging into bank account with webcam on a mandatory requirement? If so, my previous estimation was this will not happen until 2015 at least
Sorry, I don't have any covering-all statistics, some things you may induce from the numbers of Skype / MSN users, but they may be highly biased I'm afraid.
Mmmm... the statistics I'm more or less confident are that a Facebook application using a webcam, not a particularly popular sort (not even as Chat Roulette is) may easily have half a million users... (which is less then 0.1% of all Facebook users anyway