... it seems like grelber's dynamic address makes him untrackable to a very large degree, apparently subject only to which address he's using during a visit to a site that only he visits
There are at least two comments possible to put your cookie & IP# musings in perspective. The first one is about cookie content
other than IP #. This could include identifiers like hardware IDs, user name, location etc., to name just a few. The second comment pertains to data gathering channels
other than cookies, like the various trackers every web surfer attracts like smells do flies. Between these two there is more than enough bandwidth to collect perfectly distinguishing user info to circumvent the limitations of dynamic IP numbers. And I bet it's not even that hard to distinguish between different users sharing the same hardware.
Of course, I'm not saying that these channels are used all the time by every web site, but since it's so easily possible you cannot exclude it offhand. Unfortunately, for the sake of the argument here, it's impossible to qualify this surveillance without knowing the exact content of all data gathered.
