I program in java, and in a GUI program, I see no difference between that and VB as far as speed goes. The only difference is that it takes longer to start up because of loading the VM.
EDIT: Anyone remember that "mmorpg" that was being created? Someone posted it, but I forget. The players would "design" the world, and it would evolve around that..
I forget it now, but that was in Java, and it ran quite well. It also had graphics that were similar to T2's