I upgraded to OS X Mountain Lion yesterday via clean installation by downloading the OS X 10.8.2 installer from the Mac App Store and restoring it to a USB. So far, everything is working as expected, however I am experiencing higher than expected shutdown times (around the 20 seconds) in Mountain Lion. In Snow Leopard and Lion the average shutdown times that I had where in the range of 2-5 seconds. The reason of why I am reporting the slow shutdown time is that I was part of the OS X Mountain Lion Developer Preview program and at one point I had a partition in my MacBook Pro with the OS X Mountain Lion 10.8 GM Build (12A269) which was made available in the Mac App Store and the shutdown times were short and similar to those in OS X Snow Leopard and OS X Lion. Off course, given that I am very cautious when upgrading since my horrible experience with OS X Lion's release build, I waited up until yesterday to fully migrate to OS X Mountain Lion 10.8.2 since I thought that by the time of the X.X.2 release many of the kinks were being ironed out.
Anyway, I tried to solve the issue is to reinstall OS X Mountain Lion for a second time by cleaning the disk and zeroing it out on Disk Utility. I used a bootable USB installer that I made with the original installer of the app store and that has been used by many users to cleanly update their systems. The reason of why I did a second clean reinstall was to see if there was a particular app that created the issue and decided to run the computer on its factory set up before putting any new apps, before testing the computer I did a reset command so that I would boot into a new computer session and allow the OS to build its caches. The shutdown process in the reboot was slow there. I was expecting that one of my third party apps would be the reason of why my MacBook's shutdown was slow but that wasn't the case because after 30 minutes of use the shutdown time was still long without any third party apps. Due to this revelation, I decided to reboot my computer but use verbose mode because it would give me what processes are running at shutdown. Since, I could not possibly write down all the processes, I used a camera to take a picture of the verbose dialogs during shutdown. Using the same usage methodology in the previous computing session where I kept the computer running for about 30 minutes; the long shutdown was duplicated successfully.
Here are the pictures... I picked the three best pictures for clarity purposes, but they show all the available information on the screen during the complete shutdown process.
If you are having problems viewing this pictures, you can alternatively view them here.
I hope that these pictures are helpful. Now, I made a few observations on the issue, all the mentions of the hanging processes seem to be Apple derived.
Thanks for your time and assistance on this lengthy thread.