When you use Windows Vista for the first few days you see that the shut down time is not really a problem. But as time passes by you will see that slowly and gradually the shut down time of Windows Vista increases considerably and takes a toll on your patience.
So, here is a Registry tweak that helps make your Vista experience a lot better.
Step 1: Open the Registry Editor by going to the Start Menu, and typing regedit in the Search bar and then pressing Enter.
Step 2: Within the registry editor navigate to the key "HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control"
Step 3: Now, Edit the "WaitToKillServiceTimeout"="20000" by right clicking on the key and selecting Modify.
The Default setting is at 20000 milliseconds (20 seconds). Just remember that the default settings are the safest settings for your computer.
It is a bit risky to change this value as this is a system setting. But you can lower it in 4 seconds increments to see what is the best value that works for you.
Generally it is recommended not lower the value more than 3-5 seconds because if you do this you can cause your computer to shut down improperly or lose data while shutting down.
I hope this tweak was useful to you and please comment on what your observations were.