I can change my fingerprint just by dragging the window to the other monitor, since my monitors have different resolutions, and screen resolution is part of the fingerprint.
But I highly doubt any outfit who is actually using this technique as a cookie replacement is going for exact matches. They've probably defined some sort of similarity function, and they consider anybody who scores above some threshold to be the same person. That's plenty good enough for their purpose, which is to sharpen up ad delivery and deliver improved audience analytics to their clients. A few false positives or false negatives wouldn't matter.
“But I highly doubt any outfit who is actually using this technique as a cookie replacement is going for exact matches.”
That’s right. I think the panopticlick.eff.org metric is not really very good; that’s why I said “using this definition”. Bad (?) news are, the real uniqueness is much higher when taking “ambiental”/temporal continuity contexts in consideration. I question the “bad” because, well, it’s impossible to do anything in the world without leaving some kind of print. There’s a limit where the paranoia can be useful.