I recently went to an Adsense in your City event, and at their suggestion I made my ads more prominent on the most popular pages of my site, blended colors better, etc - standard stuff but it did improve my CTR and the price per click as well. No huge improvements, but very much noticeable and so well worth the time spent as I expected and earnings improvement over the long run.
However I have been used to seeing a deduction to my earnings a the end of the month of less than 1/2 of one percent. After implementing the changes in April, my earnings have been knocked down by over 3%. I figure when I see May and have all the changes I made over the course of a month in the latter part of April in place for the entire month, I am concerned that pretty much all the increase made by implementing the suggested adsense changes will be penalized away to nothing.
I am now concerned that while more prominent ads may lead to more clicks, most of those are of a type that G considers invalid, and not really good business leads that would pay out for the advertiser.
So for those of you considering re-doing your pages to make your ads more prominent and better blended, etc., it may well not be worth the effort, and you should consider that what G giveth, it often takes away.