Do AdWords and AdSense actually track users ? (Score 1)

I have two questions. I am sure somebody here can enlighten me.

1. Can Adsense ads on non-google properties actually track users, i.e. decide it's the same user that was on A, then B, then C, when none of A, B and C are google.com ? Wouldn't that require the right to access third party cookies, which most browsers forbid by default ?

2. If they can, does google actually do it ? Is there a unique user id read/written by the adsense ads, or is it accessing the google/gmail account cookie somehow ?

I tried looking into the cookies set by google, with the help of LiveHttpHeaders, but couldn't make head or tail of it... Thanks!