Initially, after having played quite a bit of World of Warcraft, I was keen on implementing the same type of auctioning system. I decided against it (for now) because a) it was always a nice-to-have, b) there weren't that many resources to trade, mostly gear, and c) it seemed like a great way for people to start farming with multiple accounts.
However, if the core of your game revolves around trading, it seems like a completely different bag entirely, and one that I don't have the experience to comment on. Because I do have a passing interest, I'll continue to lurk and see what others have to say about it.
