The Panopticlick checks how many bits of information are revealed by your browser's fingerprint: what time zone you're in, which plugins are installed, which system fonts are enabled, screen size and so on.
It turns out that, from their sample thus far, my plugins and my system fonts each independently and uniquely identifies my browser. My browser's fingerprint conveys 13.93 bits of identifying information. Switching to Google Chrome's incognito mode reduces that to 13.92 bits of identifying information. Switching to IE: increases to 14.97 bits.
Fortunately, I have nothing to hide. But for everyone else, you might want to use some browser other than your main one for your ... dodgy surfing ... so it doesn't link to other parts of your online identity. And you might want to mess with the plugins every now and again to mix things up. Or, encourage your programmer friends to write a Chrome/Ffx plugin that standardizes plugins and font lists and user agent while in private browsing mode.