Check out this months featured money maker. 
First, if you have not already, read Yahoo Quality Score - 5 Bar Experiment Part 1.
Well, this "experiment" has turned out to be rather boring as a series. I make one easy change and look back in 48 hours and boom a 4 bar quality score. DOH. So what do I do? I get ready to post about it today to find that the 4 bar quality score turned into a 5 bar this morning. DOH Again.
I guess it goes to show how easily a 5 bar quality score can be achieved with some proper tuning. A couple reasons why I think it jumped to such a high quality score:
- Removing excess keywords increases the "relevancy" of the keywords to the Ad
- Removing excess keywords can increase Click through rates
I went from hundreds of keywords down to about 50 or so keywords that were actually pulling in impressions and clicks.
I think I'm going to continue this challenge in part 3 with a new, harder experiment - maybe even in google. 
I would love to see some stats in terms of the net increase in traffic with this experiment. Maybe some percentages like… By going from X bars to Y bars I saw a xx% increase in clicks and a yy% decrease in overall CPC. Thanks for the good info, keep it coming.