One of the things that bothered me about the old US was the lack of working support for multi-core CPU's, especially when adding rings to planets or working with other simulations involving many particles.
I've noticed that with the new US2, I actually get a lower framerate with 6 cores, viewing what should be more or less the same set of calculations. An increase in general CPU load was expected, but especially with particles, they seem to really slow down my simulations beyond what seems appropriate.
Any special reason for this, or is it one of the things being ironed out?
(Other than this, I am very much enjoying and being impressed by the Alpha 13 Preview.)