Thanks for the comments, guys. I'm definitely interested in exploring co-founder relationships further. Seems to me that bringing on a "good friend" as a co-founder is a treacherous path (either take off or crash and burn), but most husband/wife, brother/sister, and very very best friends co-founder relationships seem to work out. Perhaps the extreme closeness allows the parties to communicate more openly, be more committed, or better understand and accommodate each others' weaknesses.