Although Minecraft already has 658429 registered players, due to the fact that it’s widely available on torrent and warez sites, many of these are unauthorized users.
But what’s most impressive is that at the time of writing, 155521 (23.62%) of these have already bought the game of their own free will. In the last 24 hours alone, a 11804 people registered to play, and 4910 of them bought the game. (updated statshere)
Those are good numbers regardless of whether or not everyone pays. Despite the propaganda from the RIAA, MPAA and their ilk, not every download would have been a sale, so converting a good portion that increases sales can’t be a bad thing. I’m pretty sure my HD Survival Handbook has been “pirated” but the legit sales are enough to have covered the time and effort that went into it, so I’m just not worried about something I can’t stop.
The developer also comments (somewhat obscurely I think):
“Piracy will win in the long run. It has to,” says Notch. “The alternative is too scary.”