It's not worth mentioning. Almost every case has been a coincidence and they've gone out of their way to explain the review filter (which functions similarly to Google's PageRank algorithm and attempts to filter out spammy reviews using various factors).

Each court case related to this has been thrown out.

If you trust Google to be fair with PageRank then there hasn't been any evidence that should make you more concerned about Yelp.

Business owners complain about getting demoted in Google's PageRank algorithm quite a bit, too.