Source of Overture hits

Rough % needed

[JonnyWales]

Anyone got any rough percentages as to how where their Overture hits come from? Is it predominantly Yahoo?

The reason I'm asking is that we have the number 1 result with our top terms at Yahoo but have fallen considerably with Google this update. Currently split our PPC between Overture and Adwords Select but if most Overture comes from Yahoo then perhaps they would click anyway as we are number 1 and we could then transfer spend to Adwords.