I use Yelp on occasion. I give more credence to businesses that have a large number of reviews as I feel it's more easy to spot a trend. I do not take a single good review or bad review that seriously. If numerous people are saying the same thing, "great food, mediocre service but you have to try the meatloaf" ... I find that is usually accurate. It is definitely a tool I use to try new restaurants, and mostly when I'm in an unfamiliar city.