SearchEngineWatch on the US Department for Justice attempts to get a picture of web surfing by demanding Google data:
"Getting a list of all searches in one week definitely would let US federal government dig deep into the long tail of porn searches. But then again, the sheer amount of data would be overwhelming. Do you know every variation of a term someone might use, that you're going to dig out of the hundreds of millions of searches you'd get? Oh, and be sure you filter out all the automated queries coming in from rank checking tools, while you're add it. They won't skew the data at all, nope.
Moreover, since the data is divorced from user info, you have no idea what searches are being done by children or not. In the end, you've asked for a lot of data that's not really going to help you estimate anything at all.
Far better would be to do some searches that you think children and teens are actually doing, such as by doing a survey of them. Then just go start searching on Google and the other search engines yourselves. See what actually comes up, especially when the filtering protection each service offers is enabled. That would give you plenty of data, plus it would be useful for everyone to have someone rigorously test the filtering systems that are offered. Serving subpoenas to get the data isn't necessary."