[v21]

Or, indeed, using your combination of locale, useragent, etc. These are often unique. You can test yours here: http://panopticlick.eff.org/

[jcfrei]

you're partly right - the only resolution here would be to disable javascript, which makes a great part of panopticlick work (identifying installed fonts, etc.). however I think this kind of user recognition would be an overkill for a site with so many impressions like facebook - the computational effort to assign an account to each set of features must be huge (thou maybe sometime later ... when privacy laws get more restrictive).

[thrill]

It is indeed sort of disturbing that panopticlick gives me the message "Your browser fingerprint appears to be unique among the 1,769,884 tested so far."

[NHQ]

If you add any new plugins your print would be unique again compared to your previous settings, which would make you difficult to track. Stay unique, my friends.

[v21]

Still possible, still possible. Of course, it all depends on how much they want to track you.