Most major cities, and many minor ones, have some LW-ers.

I'd be interested in details. Does it hold only inside the US? Are there some statistics which can be used to estimate the chance of at least one person coming to such a meeting?

If the LW users could specify their coordinates in their profile, and that info be automatically processed to create a world map with some reasonable resolution telling the number of LWers in a given location (say, 100x100 km grid or so), that would be a useful application.