Sun has released a Sun Service White Paper dated January 2008:
This white paper examines the current state of 3D virtual worlds and provides insight into Sun’s vision for the future of virtual worlds as they evolve with open standards and interconnected communities. The paper also provides an overview of Sun’s value proposition in this domain and describes the progress that is already being made toward open virtual worlds
This is a good read, and has a lot of information. Be sure to take note of the links on the last page if you are looking for more information on Sun’s new entry into this space.