The small business owners I know in Chicago say Yelp calls them incessantly, offering to let them take over their profile pages for $500/month (don't quote me on that price).
Their biggest issue with Yelp is that they tell their customers to go review them on Yelp. The customers do. Then Yelp deletes the reviews because the people who posted them weren't "true Yelpers." So only reviews from people who post lots of reviews are valid? WTF.