Yelp and Yahoo have partnered to show Yelp local content within Yahoo Search results.
Specifically, when you search Yahoo for local US businesses, you may see Yelp's rich reviews, ratings, photos and business information directly in the Yahoo results. This is a real partnership, I suspect with money transfer from Yahoo to Yelp, unlike with Google where they use a corkscrew to get the details.
Here is how the results look:
Forum discussion at WebmasterWorld.