Paul's recent mentions about scaling Y Combinator have prompted me to give some thought to the matter myself, but the first thing I realized is that I don't really know what's preventing it from scaling. What's the current limiting factor?

Amount of money available to invest?

How much attention you can pay to the people you fund?

The number of applications that don't suck?

And given an unlimited supply of the current limiting factor, how much bigger could you get before running up against one of the other two?