I just checked the Hoogle logs, and found a stagering 67,112 searches have been performed.
18495 of these searches were for different terms, people searched for "map" 4036. Thats quite a lot of searching!
I think those logs are since about October, which makes this just under a years data. I have no idea of what the breakdown over time is, but Hoogle 4 will have better logging, and should be able to tell me.
Update: dons tells me there have been 3849 lambdabot @hoogle searches