I implemented a couple of days ago. So far, seeing a slight CTR increase, but much lower CPC prices. I am having difficulty making them look custom though. I mostly run 728x90 text ads and the format I am seeing for the custom search ads (same size) looks more "ad like" and has the text "Ads by Google" right on top of the ads which I think is hurting CTR. The regular AdSense ads don't say "Ads by Google", just "Ad Choices" far away from the ad text copy.
Interested to know if anyone else has been using custom search ads lately in addition to netmeg.