Is a real decentralized bitcoin exchange feasible?
I can't imagine how it would work, but neither could I have imagined a decentralized p2p currency before I found out about bitcoin.
It can for the Bitcoin part and might already be possible with other cryptocurrencies like Namecoins.
For fiat money the problem is that except for cash money (which isn't easy to transfer at all) there's nearly no way to transfer it fast, cheap and irreversible to anyone in the world. MintChip looks a bit like a solution there, but I guess we'll have to wait and see what comes out of it. MasterCard also announced some kind of Webwallet today, but usually these come with "buyer protection" = merchant fees + chargeback.