Panopticlick: browser fingerprinting research
eff.org
eff.org
Interestingly, removing some of the non-standard fonts I have installed made me unique, even in private mode. This surprises me, because I have some pretty unusual fonts installed.
edit: And actually, now that I test again, it does find one other match even in non-private mode. I guess that it's counting each me as a new person each time I do it, even though I'm connecting from the same IP with the same exact browser configuration.
I use FlashBlock and Ghostery as well.