Cohabitation Agreements

A few days ago I was working on a cohabitation agreement.  I am really surprised these are not more common.  This is essentially a contractual arrangement between two individuals who plan on living together who are not married.  This can be used in the context of those who are involved in a romantic relationship or simply in the case of roommates.  It defines who is to pay what bills and what is to happen when the parties no longer wish to reside together.  I was thinking that these kind of contracts could be popular in a college town.  The only issue is that the individual would have to be twenty-one in Mississippi in order to be contractually bound to the agreement.