On the other hand, just tracking where I check in on foursquare will be kind of boring. Office, restaurants near the office (which kind of suck, compared to places even a few blocks away), airports, etc. I hope they have some kind of interesting filtering to solve that.
What I'd really like is something built on my actual purchasing history, deeper into the venue than just presence. Knowing that I always get a double double or 4x4 at innout is a pretty valid endorsement. Knowing that whenever I go to Apple stores, I buy Applecare for the products, also useful. It's useful (blinded, statistically) to other people, and presumably could be useful from a loyalty perspective, or just for personal purchase tracking, to me. (I kind of use my Amazon purchasing history like that, now. i.e. "what printer do I have in the office, so I know what toner to buy, when I'm not at the office to check".)
A payment provider (Amex for me, or maybe Square someday) is probably in the best position to do this, actually.