It was announced that Diablo III is going to have officially sanctioned cash auction houses in conjunction with in-game gold auction houses. They are also considering the sale of characters through such a service. It was also announced there will be no mod support and it will require an active internet connection (no real surprise there).
I am really disappointed with cash auction houses. That might be enough for me to pass on the game. I don't play games where people can simply throw cash at it to have the best items.