I had it and got rid of it......I have a rule, If I get traffic to my site..... Im not going to let them leave unless they click on something that makes me money(with 1 click not 2)....thus I dont do link exchanges.......If someone wants to have a link on my page they have to go threw Google Adwords...lol
Used it for a while. Got like .1% ctr and crappy cpc. Got rid of it because it was just sending away traffic.
I have it on my blog..the earnings are inconsistent coz sometimes its good sometimes it's not. But I still leave it as coz it's nice for users to have a searchbox. And adsense shows report of what words people search for.
I am going to have to disagree with the people saying they are putting the google adsense search in there for their visitors. Not only does it make a site look tacky unless perfectly places (which is really hard), the entire point of adsense is to make money. If you want to put a search function on your site, then put one on, but not adsense search. I used to have it. I got one click in about 3 months. Then I took it away and surprisingly enough, all my other adsense CTR went up. I found out that it was because the adsense search turned users away quickly because it looks tacky. Long story short - if you need a search function, put in your own. Do not use adsense search