50/50 CoFounder Split
grellas: A theoretical case is always made against the risk of deadlock, and it is a very real risk that I have seen lead to disastrous results at times.With small-business type clients, where buy-sell agreements are the norm, you would normally want to have some special provisions for breaking deadlocks as well.With startups (i.e., ventures that are intended to scale comparatively quickly over time), though, the norm is not to have such agreements and, indeed, those agreements will get in the way of normal funding, etc. and prove counter-productive in most cases.In practice, then, an overwhelming number of startups do 50/50 type arrangements and it is very rare in my experience that a problem arises with this. I would be more cautious if it is an opportunistic teaming than if you know your co-founder fairly well and have a good sense about his character. This also assumes that the contributions are equal.  50/50 is a bad idea just to achieve a sense of comity if one founder is in fact more of a contributor than the other.If you do have doubts of any kind, then you can usually achieve formal voting control even if the equity interests are otherwise equal by using a simple voting agreement to assure this. In such a case, there is a delicate balance  between formal control mechanisms and the "spirit of the deal," which you shouldn't violate lest you do damage to the important relationship you have with someone as important as a co-founder.