I've seen this used in the wild quite a few times. I'm pretty sure dome of the "universal share this button" widgets use history sniffing to put sites they know you use at the front if the list.
First? I doubt it. Also, I don't know if they were before or after these guys:
Sorry, false. We used this in 2003 for commercial purposes, as a way for Site B to verify the user had used Site A without setting a cookie.
Some years ago, some people at Stanford developed the "Safe History" Firefox extension as a means of limiting IIRC history/cache sniffing via CSS. As far as I know, the extension's currency has lapsed. The idea remains valid.