Somehow what I notice is that adsense for search pays higher per amount of click compared to content.
May be if we can talk in terms of percentage it would make picture more clear. for me its less than even 0.5%
I found it worked quite well for me a while back.. had it at the top of a forum. made about $50~ for it in a month
last months some 1000+ queries resulted in 17+$ thus totaling less than 0.47% of total revenue. my search is a service to site visitors and never intended for profit. there have been times i had double that amount per months, last year and years before.