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I haven't seen any comment on that sofar. I think it is an acceptable way to gauge user sentiment, more so than e.g. Alexa's anonymous comments (in fact in some cases it was so obvious that the site-owner was behind it, it was comical)
I'm considering using "vote" button to report spam.
I usually don't have the time and/or inclination to report spam (unless it's really blatant spam and it is in the SERPs top5) but clicking on the vote button takes only a second and I'm considering doing so.