One problem that springs to mind is that while a romantic relationship is usually one-to-one, a friendship is often part of a circle of friends - even if you'd

One problem that springs to mind is that while a romantic relationship is usually one-to-one, a friendship is often part of a circle of friends - even if you'd get along well with somebody on their own, there's no guarantee you'd fit comfortably with all their friends, to say nothing of whatever group dynamics might be involved. If there was an eHarmony-style site for friendships, it would probably involve mining social networks like Facebook for more information than just a simple personality quiz.