This has been bugging me for a while, but this morning I got to investigate it a bit further..
If I do a command such as regen, or switch between tabs/modelspace, generally anything that seems to involve a screen update, then immediately following that if I try something like a Shift-Tab type of operation, there is no response from autocad until I move the mouse. This is consistent if hardware accelertion is turned on or off, so I can't go blaming the video drivers just yet.
Anyone else get this?