I can give you one example from my firm's work. Neomonde Bakery and Deli (foursquare.com) has 1,871 total check ins from 981 people. Compare this to another local restaurant that they are partnered with, Sitti, who have 4,133 check-ins from 2,007 people.
If you compare the two I would argue a few reasons exist:
1. Sitti attracts the downtown crowd which is younger and has more first adopters.
2. Neomonde, a client, just began to invest in social media this year while Sitti, and their sister restaurants, have used social media from the beginning — including offering specials for a longer period of time.
Demographics matter, of course, but the differences also come from use.