Pros
It's in the city. Engineers are self-directed and management is horizontal. Engineers are friendly, have a strong sense of humor, and are happy. The company thoroughly has faith in that you're self-driven and will get your stuff done. This is a big gamble since some engineers may take advantage of this, but from my experience most engineers still work hard and are dedicated to the success of the company. They're liberal in terms of working from home and coming in whenever you want to. There are unique opportunities available in specific areas as this company continues to grow rapidly, especially for engineers interested in search, spam detecting, machine learning, and data mining.
Cons
The awkward division between sales and engineering which is obvious by reading other reviews. The culture and goals of each are completely different. They might as well be two companies. None of this gets explained to you. Yelp is a sad place for designers or design-minded folk, at least for the time being. Yelp hires very few real designers and leaves most design work to product managers, who typically only have a technical background. Being a public company forces product to give priority to short term revenue over building a great products. For example, banner ads are all over the site, and many of these ads are not only ugly but directly contradict Yelp's mission of connecting people with local businesses (e.g. Taco Bell). In many ways Yelp is very corporate, as much as they would hate to admit it. Terribly inefficient workflows and outdated internal tools are maintained despite constant griping. Important decisions often go unquestioned. Quality is not job one. The politics of priority or "MVP" prevent good ideas from even seeing the light of day.