Joystiq just posted a small part of Jay Wilson's GDC talk about Diablo 3. Some excerpts can be found below and you can read the whole article here. We will be posting a video if one such is posted. The post also mentions that Diablo has about 1 million players a day.
But he said that once the game went live, Blizzard realized it was completely wrong about those last two points. It turns out that nearly every one of the game's players (of which there are still about 1 million per day, and about 3 million per month, according to Wilson) made use of either house, and that over 50 percent of players used it regularly. That, said Wilson, made money a much higher motivator than the game's original motivation to simply kill Diablo, and "damaged item rewards" in the game. While a lot of the buzz around the game attacked the real money Auction House, "gold does much more damage than the other one does," according to Wilson, because more players use it and prices fluctuate much more.
"I think we would turn it off if we could," Wilson said during his talk. But the problem is "not as easy as that;" with all of Blizzard's current players, he says the company "has no idea" how many players like the system or hate it.