That's true -- there have been several projects making use of the CSS :visited history sniffing technique. The method itself was originally reported in early 2000. See http://whattheinternetknowsaboutyou.com/docs/details.html#re...

It looks like it's working now even without JS. The history detection method itself doesn't need JavaScript at all; see http://whattheinternetknowsaboutyou.com/docs/details.html