Charles Arthur writes about Gowalla and Foursquare here; basically deciding they're pointless. You'd have thought that post blogging, MySpace, Facebook, Twitter etc people would pause for thought before deciding things had no point. But he's a smart man so it's worth examining why he'd say that, especially as a lot of other smart people (and me) do find them pointful enough to play with.
I suspect one aspect of this is the way web and mobile stuff lowers so many barriers. It's lowered the cost, effort and skills required to build tools, express yourself, connect to people etc etc. All that. It's also lowered the amount of point something needs to have to be worth playing with. It's lowered the point point. Using Foursquare or Gowalla represents such a minimal amount of effort and energy - normally in a moment of your day when you're not doing anything else - that you only need a tiny amount of reward for it to be worthwhile. And, actually, for quite a lot of people, quite a lot of the point is in seeing how much point there is.
Playing with something like Gowalla or Foursquare is worth doing - to see if it's worth doing.
And because it's so little effort to do it you're prepared to give it a bit of time, try it for a few weeks, see how it fits in your life - rather than just doing the brief evaluation a professional reviewer traditionally used to do.
Anyway, hopefully you get my point. Ha!