[michaelt]

People would either (a) pay to place ads on sites they knew had a decent amount of traffic just from reputation, or (b) would hire ad-buying companies which made it their business to know what different sites' ad space is worth.

Needless to say, this could be inconvenient for the adwords-make-me-five-bucks-a-month scale sites. It'd work out OK for the New York Times-es of the world though.