OS X :: Long Shutdown Time Of MacBook Pro (10.5.8) - How To Make It Smooth

I am having issues with the shutdown time of my MBP. Namely, until couple of days ago, everything was fine and the shutdown process lasted for about 5 seconds tops. The other day, when I was about to go to bed and shut it down, the shutdown took unusually long time to execute. From that day on, every shutdown is the same. It lasts for about 40 seconds. This is kinda not that funny, because from time to time, like every couple of months the shutdown would be long like this, but the next shutdown would be very short. I consider this to be normal, as far as I read the various forum posts. What bothers me is that since couple of days ago, every shutdown lasts for about 45 seconds and it is not a problem, since the computer works fine, but is kinda irritating. I also have to mention that no major changes (installation or removal of programs) have been performed prior to this issue, and that my login items list is empty.

I have tried the following:

* Zapping the PRAM
* Executing various Onyx scripts, and used Onyx it to clean various caches.
* Reading, verifying and repairing permission using Disk Utility.


None worked for me.

I am pretty sure there are numerous threads about this or similar subject, but I have not found the one that describes this issue that I have.