I was just killing some time over at digg and found an interesting service for instant messaging. It's called radiusIM. From the look of things it just shows you other members by location. While I think this is quite cool and could be useful for meeting new people based on location.
I don't think it will be catching on. For starters it does not appear to integrate with an IM client, as it i,which means having to log-on to a website for the service. This lack of integration also most likely means it will not know your location automagicaly if you sign in at a different location so for those who travel frequently would have to update their location if they want to be accurately reflecting their current locale. I don't know about you but I don't really care if someone knows what part of town I live in, but I am a bit more concerned if my specific block or neighborhood is being broadcasts or made available to anyone who wants to know.

I haven't signed up for the service. So I don't know if there are any privacy options or any other options for the application. But I don't see a very practical or useful reason to use it aside from just being social with people nearby or in a specific area that one may be interested in.

Also I noticed their flash demo uses only names of South Park characters...