I have read and heard about people complaining about sandbox here. Although it's a good technique used by G to filter out spam sites but unfortunately my site is also suffering from the sandbox effect. So this is what I present.
I propose google to combine the ad-sense smart-pricing along with SERPS. Smart-pricing calculates the click quality and in turn also somwhat tells about the site quality. So google could use this technique to get higher quality sites out of the sandbox effect and possibly even for PR and positioning on the SERPS.
Well this would only effect sites using ad-sense but it could also be a good way for G to promote ad-sense.
I haven't thought of it in detail. But it's good food for thought.