They keep vanilla search info for 18 months. they keep google map search info indefinitely, they keep certain image, and picasa search info indefinitely, etc. it STRONGLY depends on the info you are concerned. it was an enormous pain in the ass to get dad's phone number delisted (he didn't want it on google's listings, wasn't on phone book listing) they've streamlined the process since, but some of their bureaucracy is worse than DMV.
I use google all the time, yahoo sucks. I don't really care what they do with my searches, because I am not looking for bomb instructions or child p()rn.
One might argue that all corporations are evil. And it's because of shit like this one might argue such a thing.