Who knows what's true here, but I know a lot of businesses that hate Yelp because the business can't control the tone of the publicity. I also know a couple people that game Yelp, by emailing users and bribing to change reviews.

Yelp's the web 2 service that's actually made a difference in my life, but these things always have shady underbellies (e.g. Google, SEO, click fraud).