Great UX team article on UXmatters.com by Pabini Gabriel-Petit. The article does a great job outlining real world problems such as 'throwing docs over the fence', the discrete discipline roles and how they should work together. While organizational roles differ by organization, I've found that the more disciplines represented in the process, the more innovative the UX solution. As Scott Berkun notes in The Myths of Innovation great innovations build on others work and collaboration.