Andrew has some great hints over on his blog about 7 questions to ask a co-founder.  It’s more of a list of preparatory steps and things to think about.  Having gone through this already, it’s very true.  Partnering in business is like partnering in marriage and you quickly become attached at the hip.  For me, it’s been a great experience, but you really need to evaluate who you are going to partner with before you start on any adventure.