The database is limited in its current state, both in number of registrants and scope. You may find yourself with a Wii full of friends, but it's impossible to know which ones will stick without much trial and error. In this case, real-world location isn't as important as play-style or genre preference. A few more fields of required data and MapWii could go a long way toward hastening the 'matchmaking' process.
See also: Web sites step up to connect Wii owners