Ok so I had time at work after all, here is the post from anadtech I referred to that works perfectly and does not involve editing the registry directly.

"As I suspected, this is a bug that was supposedly fixed in SP3 but apparently has been re-introduced in one of the latest MS updates as others appear to be seeing the exact same problem. The problem (MS KB Q285192: Userenv failing to unload profile on shutdown) is mentioned here and of course I was seeing a ton of these in the event viewer: Q285192

The workaround that I applied for anyone interested:

Run gpedit.msc: Start -> Run -> gpedit.msc

Then: Local Computer Policy -> Computer Configuration -> Administrative Templates -> System -> Logon -> Maximum retries to unload and update user profile (right click and select Properties). Then select Enabled and set the value to 0.

Both of my 440BX-based machines now shutdown within 10 seconds after selecting a shutdown... "

Thanks to HeinekinMan on anandtech.