You've disabled cookies and opened a private browsing window, so you're confident nobody can see what you're visiting on the web. The Electronic Frontier Foundation begs to differ, and their Panopticlick web app will show you how trackable you really are.
No matter what reason you might have to wonder if a site owner, IT administrator or other snoopy type can see where you've been, the EFF's Panopticon tool is an eye-opening look at how identifiable you really are online. Using a Chromium build on Linux, for example, means that you're travelling the web with a certain set of installed fonts, usable plugins and browser identifications, and from a particular time zone and operating system. Put it all together, and if you were wondering whether SuperPanMegaCorp could tell whether you hit two of their different sites, well — yeah, they probably can guess it's you.
Now that you're sufficiently reminded of the web's voyeuristic capabilities, you can read up on the theories and tech behind Panopticlick at the EFF's explainer. If there are other aspects of browsing that you wish more browsers were aware of, tell us about it in the comments.