I have been seeing something that I think has changed with 2010. I have noticed quite a delay in reaction when I hold the Ctrl key and use the MMB to pan. I tend to move quickly and there is a delay such that the model doesn't move. It appears to be somewhat related to the number of parts in the model. An assy with only 500 parts is quite noticeable but one with 2 parts not nearly as much.
Then I found something interesting. Open Task Manager in order to watch CPU time. Then in SW, pan your assy with the Ctrl key, then stop - the CPU usage goes up when moving (as it should) and then goes down when you stop (as it should). But then just press and hold the Ctrl key - the CPU usage goes all the way back up. (I did not see as much of this on the XP32 machine.)
Another interesting aspect is that if I do a RMB and pick Pan, and then pan with the LMB, it moves fine - no delay at all.
Anyone else verify this? I tried it on my XP64 machine and also an XP32 machine - same thing.