Diablo 3 will have an optional real-money auction house in which players can sell items and characters for real money. There will be a seperate auction house in place that does in game currency instead of real cash as well. To use the real-money auction house the player will have to pay a fee per listing. The fees won't scale on the price of the item so blizzard won't make more money on rare items and is there to discourage listing a lot of useless items. To encourage the use of this, players will be given a certain number of free listings each week.
When the item sells, the player can get a blizzard credit for use in anything blizzard related (shirts, Wow subs, other auctions in diablo 3) or get charged a fee and payed with real cash using their payment partner (most likely paypal, but unconfirmed yet). Players can also sell their characters as well for quite a chunk of money if it's anything comparable to selling a character on World of Warcraft. Blizzard has made it clear that this will not be spreading to World of Warcraft as the loot structure there is very different.
I will assume that the idea behind this is to create a way to capitalize off of people selling items and characters by providing a method for it in game. In addition, by having an in-game option, people are less likely to go to key logging websites when trying to buy characters and items. Overall, I think the idea is a mix of good and bad, and can provide a way for hardcore farmers to earn a little extra cash.
On a related note, Diablo 3 will also require a constant internet connection to play in both single and multiplayer (Ubisoft anyone?). Blizzard states this is due to the fact that stats carry over from the seemless multiplayer and single player experiences.
I'm curious, what are your thoughts on this new style of auction house and the always-on DRM?