I was not aware that the takeup of the toolbar amongst joe public was that great yet.
Also, click-through rate is not a measure of user satisfaction. Whilst I don't doubt Google have considered this technology, I do doubt that it would improve already good results. Of course, with current results .....
Also, using click-through rates to modify SERPS is rather like positive feedback. Normally this is to be avoided since it reduces stability, however, with search engines, ironically, it would cause greater stability. Is that a good thing?