Pros
Yelp has a great culture and the people you work with are awesome. The website itself is very useful, and the products are pretty good. You also can gain valuable training for sales, CRM, etc.
Cons
The job itself in a word.. sucks. you cold call small business owners all day, trying to pitch them our ad product which may/may not work for them. the people you talk to either love or hate yelp, and often times are very difficult to work with. many of the people you interact with don't speak english, you get hung up on a lot, and some people are just plain dumb. there also isn't much career advancement outside of sales-- management hasn't yet really figured out how to develop someone's career there who has put in their time and wanted to get out of sales, which is why a lot of people quit after a year or 2 (if they can even last that long!)