People have been asking for this since Adsense started. This should make advertisers much happier. On the other hand, it COULD hurt publishers who were benefitting from high search bids filtering to their content.
However, I know many advertisers who cancelled putting their ads on the content network because they couldn’t change it, now that they can, I imagine the amount of ads available will drastically go up, and thus raise revenue for Adsense publishers.