For example, just this morning someone paid $10 for an album after Googling lelia broussard torrent. A bit later, a fan plunked down $17 after searching for murder by death, skeletons in the closet, mediafire.

Where do they get this data?

From the referer header. If someone clicks from google the search fields are transmitted in the referrer.

If this bothers you, use duckduckgo.com which has a special bounce-page to hide this info.

> If this bothers you, use duckduckgo.com which has a special bounce-page to hide this info.

Or something like RefControl http://www.stardrifter.org/refcontrol/ for Firefox and control what and to whom you send.

Or use https search, google doesn't even require you to go to encrypted.google.com [1]

[1] https://www.google.com/

Won't the referrer still be sent if the target site is available over SSL?

Yes, but the referrer will only be google.com.

Google SSL uses POST for the search query parameters, so the referrer URI w/ GET parameters will not leak your search terms.