But the question is if GA and others actually accept these kind of requests: remember that someone with such and such UA (or IP, or whatever) has visited that website? And if people actually use it? I still have my doubts that tracking someone by UA is possible — there will be collisions for the large part of the market — but that some analytics service is actually doing it? It's easy to track me if Google can "reach" to the client side when visiting some website: they can use cookies, all HTTP-request data, even flash-cookies maybe. It's a no brainer to track individual with information like this. But guessing who is who just by UA? This doesn't seem that trivial, so I wonder if they really do that.