I like the idea of being able to see who you are geographically close to, but I think modifying nicknames would certainly clutter the chatterbox a lot. So how about this way of doing it: have a node where you can enter your current location, and then a page where you can see, in alphabetical order, all the locations that people have entered. So not everyone would have to participate, but those who did would be listed there, and you could check that page to see if there were other people in the same area or city, without imposing the information on others using perlmonks.org.
BTW, right now I'm in Athens (Greece) for a conference, until Wednesday. Any monks near in the area? I won't have net access after today, but I'm staying at the Athens Plaza hotel, give me a call and we can go have dinner or at least a beer :-)
--ZZamboni