We've not yet upgraded, but I've done some heavy evaluation of Asset 7 and NS 7.
After attending Vision I'd suggest investigating and preparing to migrate after Symantec Management Platform 7.1 (formerly NS) is released.
I would also seriously consider Asset 7 at this time as well.
On the topic of Service Desk 7 I would tottally recommend it. It's a really cool solution and if you already own Asset the solutions are integrated with some very cool workflows that could be super useful in many environments. It
can run on a Virtual environment, but I wouldn't recommend it due to the memory requirements, but it can run in there.