Yelp is one of the older location based social networks. They have been around since 2004 and are more a social review service than a location based social network, still because they connect local businesses with customers I believe they should fall into this category.
The concept behind this social reviews site is simple: connect people with great businesses. You go to a sushi restaurant that you like and then afterwords give it a good review. The more positive reviews the higher the restaurant will place in Yelp searches for sushi restaurants.
Then when people find the restaurant they can read customers unbiased reviews, such as yours toward the place. Because Yelp has locations across the United States, Canada, Britain, Ireland, and France you can find reviews from your peers here. Additionally, owners have a special feature that allows them to respond to customers and positive (and sometimes not so positive) comments on their restaurants.
A small business can use this as a marketing resource, because they will benefit from the quality customer service that will in turn attract lots of positive attention. The more people who positively review your company can lead to more business.
Additionally, Yelp also has a tremendous back end solution available to location based small business owners that allows them to participate with their customers feedback as stated before as well as create offers for their business. 10% off this week on all cinnamon sticks(now I am hungry)? Display on it Yelp for additional exposure.
You can then track your hits to your offer and your business on Yelp through their tracking software, which lets you see the number of monthly visitors see your business online along with new reviews and comments of your business. There is also a business profile tracker to show businesses what else they can add to their Yelp profiles to give a complete picture of their company.
The final item is a Yelp badge, which you can display on your website. Much like I have a Facebook badge to my fan page and also a badge to my Twitter account you can use one for Yelp to connect the two sites.
The one downside to Yelp is that they are not as mobile friendly as other location based social networks, such as Foursquare. While they do have an app on my Blackberry that allows me to search for restaurants in the area, they do not have the ability as far as I could tell from fooling around with the app to allow me to create a review directly from the mobile application.
All in all , this social review site is very useful, because 30 million plus people visit it every month providing it with a lot of heft for any business. This location based social network provides customers with an accurate description of your business.