Getting 70 or so high caliber founders and pooling their respective strengths is a huge advantage. Usually the press talks about the valuable advice and connections offered by the YC partners - this is just as big though. Everyone gets advice from the best sys admins, designers, etc, from across the batch.<p>The biggest successes online always seem to have some sort of marketplace for a business model - Google, Ebay, Paypal, etc. Not surprisingly, as YC seems on track to becoming a big hit, they have managed to find such a model. They are becoming a market place for top founders to network and exchange ideas. This would be very hard to recreate in an unstructured environment (like a co-op), because trust is essential.