Google's log of searches is an amazingly useful feature. Sometimes I google for some obscure library, find it, go to lunch, and then completely forget what it was called or what search terms I used to find it. With the search history, this is not a problem.

I also use Google search for package tracking, and it's nice to get the numbers out of the search history instead of the merchant's site.

I know everyone wants to think that Google is collecting this information so that they know who to come for first when they take over the world... but it's also possible that the feature exists simply because it's useful.