Earlier quoted context omitted.
How about exponentially increasing ban times, instead of a life-time ban after the third strike? (Perhaps with even a cooling off period, if you behave well for some time.)
That's a brilliant idea, really. I wonder how we could generate an economic incentive for Google to adopt it.
Want to incentivize Google? Convince Bing to implement it and see if Adsense customers convert as a result. If I felt Bing was treating their customers/vendors (ads is a really weird relationship :) better, I would consider using it (since as a search product it has approached Google pretty close).