After have applied those commands I must say my shutdown times have improved from 20 seconds (almost always) to 2 seconds on my 15" rMBP 2.6 (10.8.3)!!!
Two days that I'm testing and 2 days that my mac shutdown almost instantly...
Hope those commands will fix shutdown "forever"!
Thanks a lot Razmarino!
P.S. @ Razmarino: can I repair disk permissions again after those commands, or a disk permission repair will cancel commands effect? I ask to you because, if I do a verify disk permission, just those .plist permissions are not correct....
Bye,
Andrea