At first though I'm really not a fan of this. Here are a couple of thoughts:
1) The vast majority of items on the AH are going to be on the Real Money one. Who doesn't want to sell their item for real money. I hope this doesn't force everyone to use real money.
2) If the market goes sour because of the influx of items from farmers, will Blizzard artificially change the market so they make more money? i.e. change drop rates, etc
3) The screenshots I'm seeing have items at like $5.00. And while this is obviously a screenshot from a limited market, is there a limit to what you can sell an item for?
One thing I know for sure is that I'm not as hyped about the game as I was. Anytime they take a fun game and make it into "work" is a bad thing. I can see a lot of contention amongst friends as an item that might be worth hundreds of real dollars drops and now one or the other gets screwed. The other problem is now friends might not freely give items as they now have a real worth associated to them.
1- if "everyone" uses real money, it's the same as nobody using real money. As long as you don't buy more from the AH than you sell, it's a zero sum game (except blizzard's 5% cut). You sell a robe of wizardly might for $5, and buy a battle-axe of warrior's doom for $5, it's effectivly no different from selling the robe for 50k gold and buying the axe for 50k gold. The only reason you would "need" money to use the AH is if you buy more than you sell. Which is how it works already in similar games.
2- It's natural for the market value of items to drop over time. Early on, the best items will be extremely rare, but 6 months after release those same items will be more common. I don't think there is anything blizzard can do to prevent this, nor should they even try. It's a natural lifecycle for this sort of market.
3- It's an auction house. The seller can set a buyout, otherwise there should be no limit to the bidding. I suppose blizzard will probably have some hard cap to prevent fraud or money laundering through the system, but it'll probably be higher than anyone would dream on spending for a virtual item.
(4)- Contention over virtual items already occur. Legit market or not, some things in World of Warcraft are worth the equivalent of $100 or more. If you and your friends can look past that and work things out, great. If not, you will screw your friend or he will screw you. Whether it's a rare item in diablo 3 with a market value of $15, or a rare BoE epic in WoW that auctions for 20k+ gold (which could be worth $15), it's the same either way although it's harder to monetize the wow gold.