I have no complaints about Adsense, but I do have an observation. I have a site that has had the same ad layout for a year.
In that time the Link Unit Impression RPM has gone down to about 40% of what it once was.
I believe this is due to the fact that they started putting the label “sponsored” or “sponsored searches” on them in June, and have begun to try different designs with them in the last few months.
This observation is based on 800,000 impressions.
Google can do whatever they want, I don’t want visitors clicking on something unless they know it’s an ad. It’s just a shame, because I really liked these little units and they really produced.