HKEY_LOCAL_MACHINE\Software\Microsoft\Windows\CurrentVersion\Internet Settings\User Agent\Post Platform
One more thing I wanted to add on the subject. At this section of the registry, you can add anything you might wish. (Not sure about max characters, but what you might add there can have spaces and such.)
Adding something there would be a way of having a unique signature, dropped into the webserver logs, saying you were by for a visit.