Sometimes freezes when shutting down

Hello everyone
I own a Macbook Pro 13'' and sometimes, although rarely, it freezes when shutting down, it appears that light-blue screen that always appears before the screen gets black but now it stays at that blue screen and wont move on, besides, it has that spinning wheel (not the cursor spinning wheel, but yes that one that appears below the apple logo when starting up the macbook).
I've already tried to repair the disk several times with onyx and disk utility but it always says the disk is fine, and I've also done the apple hardware test but no errors were found.
I've already considered to reinstall OS x but that seems like a drastic measure, because apart from the freezing when shutting down, my macbook is totally fine.
I would apreciate any suggestion and advice you can give me about how to solve this problem.

Thank you,
Slash_93

What version of OS X are you running?

What apps are still running when you shut down?

I'm running Mac OS X 10.6.2.
Concerning the apps I'm running when I shut it down, well, that's a good question.
Usually I close the applications before shutting the macbook down, but many times i forget or i'm in a hurry, so I leave them open. I don't know for sure which, but I can tell you that probably Messenger for Mac, office for mac and itunes are sometimes open when i shut down.

Most of the time it seems to be caused by an app that is/was attempting to access the internet at the time you shut down.

Mail, Messenger, etc... but not always.

Mail has definitely had this issue in previous versions of OS X, but seems to be fixed currently.

have you updated your system recently? maybe it didn't finish properly, it can happen ... try downloading the last update and running it manually

Everything is up to date, I always install the updates as soon as they are available.
The big problem here is that everytime it freezes up, I have to force shut it down, and I know that that's not very healthy for the computer

Hey I had the same problem my macbook would take almost 2 mins to shut down after looking through my system library I found I had a bad file with my printer which would cause my laptop to wait as it tried to close it after uninstalling my printer and reinstalling it my laptop is back to its normal self.
So try looking through the system files you may have something starting up that is bad

Actually I installed my printer driver and software long after this problem started, I've just done an Erase and Install (i backed up all my files using time machine) and I'm waiting to see if the problem is solved ( Archive and Install didn't solve the problem).