Provide separate discussion areas (subreddits?) for geographic subcommunities.
Google Groups and Meetup.com are currently used for this purpose by some, but this is not the most elegant solution. It sprawls LW content beyond the main site, requires learning how to use different interfaces, and puts us at the mercy of outside companies. The possibility of karma would also encourage more discussion among these groups.
Currently, there is a way for filtering LW content to view only submissions from people on one’s friends list (http://lesswrong.com/r/friends/).
This only displays original posts, though. I would like to see this extended to comments as well.