I just went on to AskPatents and tried my hand at it:
http://patents.stackexchange.com/questions/197/prior-art-for...I'm not doing anything close to as good a job as a patent examiner would do, but with about an hour of work I (hopefully) was able to start pointing to some prior art that could get an examiner quickly up to speed on what the state of the art is.
I agree the amount of work involved to comprehensively invalidate a patent would be days - hopefully a group can do the same with shorter time contributions.