Search can do well on some sites. It depends on the sites topic and what people are searching for. I have found that the CTR on Adsense search is quite high but the trick is getting people to search. One good thing about running Adsense for search is you can see what terms people are searching for on your site.
i use it on my site mostly because my CMS sucks the CPU juice when users search the site, so i'd rather use Google's CPU.. Earnings vary all over the place, but it's nowhere near what Adsense for Content earns.. Like the usedMac said, it's going to depend a lot on what your niche is and what they're searching for..
Two good reasons for using adsense for search. Just the kick I needed. P.S. I haven't been using it, but will give it a try now.