However, this might just change my mind: check out "Get London Reading," an iPhone app that tells you which books were set where in London. This means that I have to find someone who has an iPhone and become good enough friends with him that I can invite him on my litnerd tour of London, but not good enough friends that I have to invite him to Thanksgiving dinner--because I freaking hate those people. (You know the ones I mean.)
Denver has something kind of similar, though, although not nearly as cool. If you walk around Denver, you occasionally come across a sign with a phone number on it, and if you call it, it gives you the history of the neighborhood you're in, although it's kind of a pain to find the signs in the first place and... yeah, I really need to make friends with someone with an iPhone.