I am now running 10.6.3. When I booted my MBP3.1, 2.4Ghz, a few minutes ago it took 52 seconds from the time the chime sounded until the Menu Bar was fully populated. How long it takes my MBP to shutdown seems to be a function of how many apps I have loaded. When i shutdown earlier, I was running Fusion in Unity mode with two Windows apps open. In addition I had five open OS X apps. The shutdown required the better part of two minutes, most of which was taken up with shutting down the open apps and most of that time was spent on closing Fusion.
EDIT: After posting the foregoing, I closed all open apps before shutting down the MBP. With no open apps to be closed, the shutdown took 22 seconds.