1. Citations – Google uses citations for Local Business Listings in the same way it uses Inbound Links for its local ranking algorithms. The more citations you have the higher probability you have to rank well in Google Local Business. Foursquare allows you to add your address and phone number to your listing which is enough to qualify as a citation for this purpose. Tom Critchlow has some awesome information about Google Local here.
2. Link Building – You can leave tips on venue pages. Not many people have noticed that when you leave a tip you have the option to specify a link. These links are followed. For an example of these links take a look at my comment on the PushON Foursquare listing.
3. Bing Maps – Bing recently announced that they’re going to be including Foursquare data in their maps. There is no reason why Google and other mapping website won’t start doing it.

Got another reason? Let me know!

However now they include the users real name as well as their username.

This is another opportunity great for both brands and people to own more of the SERPs for their names.