Yesterday i found some interesting news-item about "Browser Fingerprinting"
Even without cookies, it seems to be possible to identify a lot of users uniquely by other client data.
You can visit the project description here:
https://www.eff.org/deeplinks/2010/01/primer-information-theory-and-privacy
To test if they can identify your browser uniquely among hundreds of thousands visit this url:
https://panopticlick.eff.org/
The site is a bit slow atm, but it`s a quite interesting project
My browser seems to be unique \o/