According to Bloody Disgusting, a friend of a friend of a friend's wife's sister got wind that Paul Thomas Anderson's next project will be a horror film. At the rate he works, we may not know if this is true until 2012, but it's curious nonetheless.
I heard the same thing about Spike Jonze and Charlie Kaufman a few years back, but that seems to have fizzled. Maybe it's just the stock answer filmmakers give, nowadays, when the're faced with the "So what are you doing next?" question.