Seems a fine idea to me so long as nobody tries to make it OFFICIAL or worm it around to put a corner on game lore or history that might 'lock out' other people. ("That mysterious fire in Whatsit City in the Year of the Badger that's mentioned in the game intro? Totally our guys!" sort of thing.) Sounds like a fun way to add depth, character ties, and background provided nobody tries to make it any more than a 100% in-character association tool. It'd be a good vehicle to get plots going, or to bring more people into a story in progress as well as give characters common grounds and interests. Though my character concept is loose at present, I could totally see him being part of some sort of cartographer's or explorer's guild.
