Robert_Charlton - 11:12 pm on Oct 2, 2010 (gmt 0)
Some discussion from last year about Yelp here....
Yelp Makes Changes To Address Criticism
There's no question in my mind that there were rogue reviews posted on Yelp. I haven't seen such reviews myself on Google, but I have seen lots of other deliberate sabotage on Place Pages. Anonymous "user" reviews are a can of worms everywhere, and there's no reason that Google should be immune.
While Google, at least to a limited degree, is aware of the problem of negative reviews, they are putting a lot on a small business owner, many of whom are not web savvy and may not even be aware that Place Pages exist... but then so is every other site that allows unmoderated reviews.
Some related discussion here...
Google Now Lets You Respond To Reviews On Google Places