As virtual reality (VR) continues to gain prominence as a medium for artistic expression, a growing number of projects explore the use of VR for musical interaction design. In this paper, we discuss the concept of VIMEs (Virtual Interfaces for Musical Expression) through four case studies that explore different aspects of musical interactions in virtual environments. We then describe a user study designed to evaluate these VIMEs in terms of various usability considerations, such as immersion, perception of control, learnability and physical effort. We offer the results of the study, articulating the relationship between the design of a VIME and the various performance behaviors observed among its users. Finally, we discuss how these results, combined with recent developments in VR technology, can inform the design of new VIMEs.