We added Panopticlick-inspired user fingerprinting to SnowPlow recently - as far as we know, we're the first analytics package to make user fingerprinting generally available. If you're interested in the implementation, it's here:
Way to make a name for yourself under the Be Evil brand--democratizing access to abusive user-hostile technology. It has the same feel as an open access community meth lab.
https://github.com/snowplow/snowplow/blob/master/1-trackers/...
I'm skeptical of its utility on its own - though when you add timezone, IP address and screen resolution, it may start to get mostly-unique.
Anyway we're waiting on some of out bigger users (millions of page views per day) to report back on its uniqueness - should be interesting...