So it seems someone has finally gotten around to setting up a Dodgeball-like service for the UK. It be called BuddyPing.

Basically it allows you to register your location and, depending on your settings, notify and be notified when you're within a certain distance of your friends. Quite cool if you happen to be in the next pub down. Figured I'd have a play with it, so I've registered. Let me know if you sign up and I'll stick yer on me list.

Edit: Although, damn, is their email being slow. I'll be registered eventually...
Justin @ BuddyPing has now updated the FAQ to include information about costs.

9. How much does it cost to use buddyPing?

For the foreseeable future buddyPing will be free. We are still in the testing stage at the moment, but as time goes on and new users come on board, we will need to charge for certain aspects. Needless to say, all users will be notified of any changes when they occur.