M-of-N transactions solve most of the trust problems with online marketplaces without having to cede total authority to the escrow service. If you want to favor the buyer in disputes a la paypal, that's easy, but the worst thing that can happen in the case of a false positive (from the seller's perspective) is the loss of a single transaction, rather than having an entire account frozen.
M of N is useful, yes. All I'm saying is that reversibility is an important part of online transactions, and you need _some_ kind of mechanism here to facilitate trust.
