This is a project that was started by the EFF (Electronic Frontier Foundation, an organization that champions privacy and rights online among other things) to raise awareness of just how unique--that is, trackable--your browser is. If you're curious, measure yourself here. Out of the one and a half million browsers tested, apparently my Chromium installation under Ubuntu is unique in terms of browser plugins and system fonts.
Other metrics of interest are things like the state of JavaScript among visitors to the site. It appears that about one in 3 browsers have JavaScript disabled either outright or with a plugin such as NoScript (for Firefox). I'm somewhat surprised that this number is so low; considering that the majority of visitors to the EFF's Panopticlick site are undoubtedly tech savvy or have tech savvy friends, I would have expected this number to be higher. Perhaps this is a side effect of the increasing popularity of browsers like Google Chrome among technically-minded individuals which enable JavaScript (and plugins) by default. However, I still maintain that the absolute safest way to browse is with the latest version of Mozilla Firefox with NoScript and FlashBlock installed (AdBlock only blocks ads, it does not block other Flash-based entities).
Attached is a screenshot of what this site reports of my Chromium install under Ubuntu (I may post more later for those who are painfully curious).