Thanks for the quick response. The slow quit would happen in either of the scenarios you describe. However, the good news is that I may have inadvertantly solved the problem.
I set up this machine to drive two displays off of one video card. All our other machines have two cards, but I installed an ATI 8500 which can drive two monitors, so I thought I would give it a try (our older ATI secondary cards require a workaround in OS X, kind of a pain).
My initial setup had the gray startup screen showing up on the secondary monitor. This was the setup that produced the slow quit behavior. When I switched ports on the card I got the startup on the main monitor and also fixed VW (quitting is now instantaneous).
I don't know if there is a cause and effect relationship here, but the only other thing I did that I can think of is repair permissions a few times. In any case I'm not complaining!