UPDATE (11:49am): Looks like Sony took down the listing. Bummer.
Original post follows:
The PlayStation Store is listing Uncharted 3 for free right now. This isn't just for PS Plus members; anyone with a PlayStation Network account can download the third game in Nathan Drake's adventures without paying a cent.
Looks like this is only the single-player portion of the game, and it's only available to North American users.
There's nothing about this on the PlayStation Blog, and we haven't heard anything from Sony about Uncharted 3 going free to all users, so this may be a mistake. Get it while you can.