[kbenson]

Just based on a random seed set when the browser loads and the domain name being loaded (that is, external resource requests get the values for the sourcing page domain, which is already tracked in browsers for security purposes). You'll get persistent per-domain values per browser run. If they can already track you definitively beyond that (bookie, session, etc), you're not hurting yourself at all by doing it, but it will possibly help with all the other cases.