Have you tried using Yahoo Search Marketing lately?  I always disliked it in the past.  It never performed very well for me.

Now I may be changing my tune.  It all depends on 4%.  If you have at least a 4% clickthrough rate your quality score will be pretty good.

So keep this in mind when you are writing your ads.  You have to write them to get a high CTR (clickthrough rate) and a high conversion rate.