The configurability and networking abilities of digital musical instruments increases the possibilities for collaboration in musical performances. Computer music ensembles such as laptop orchestras are becoming increasingly common and provide laboratories for the exploration of these possibilities. However, much of the literature regarding the creation of DMIs has been focused on individual expressivity, and their potential for collaborative performance has been under-utilized. This paper makes the case for the benefits of an approach to digital musical instrument design that begins with their collaborative potential, examines several frameworks and sets of principles for the creation of digital musical instruments, and proposes a dimension space representation of collaborative approaches which can be used to evaluate and guide future DMI creation. Several examples of DMIs and compositions are then evaluated and discussed in the context of this dimension space.