one of the problems with p2p exchanges is the part where fiat is involved = bank accounts that need to hold the money of the traders. another problem is the complexity of building and testing such systems.
imho the solution will come when the forex guys decide to enter the market. they have all the legal paperwork of handling people money and have proven forex trading systems that can probably be modified easily for bitcoin trading. not to mention they have all their users that they can easily convert into bitcoin trading.