AndyA - 11:13 pm on Apr 29, 2010 (gmt 0)
When the network is bursting at the seams with publishers eager to fill unsold inventory
Don't forget about the publishers who sign up thinking AS is going to make them a fortune, then drop it when they see it doesn't.
And consider the publishers who are now unhappy because click throughs have dropped, some are pulling AS completely or limiting impressions until the issue resolves itself. Both will impact Google's income as well, since fewer impressions = fewer clicks = less income.