If you have a shop, you should register for an account at Four Square. The advantage of Four Square is that it encourage people to share their favorite place so if people like the products your shop offer, they can share it with their friends easily from Foursquare. Foursquare has a good impact on your online business' SEO because those who have Foursquare profiles will easily get crawled by the search engines. Hence, Foursquare can have direct impact on the ranking of your business on the SERP result. Make sure every information in your Foursquare profile is correct and up to date for example you must make sure the location and address is correct because the crawler will use this information to rank your business in the local search.