Apparently the LUAFV driver, which controls UAC in Vista, can cause latency issues if the feature is disabled.
Once UAC is disabled, a registry tweak that disables the driver in question needs to be applied if the user wants to have more solid boot times back (improved boot times obviously vary from machine to machine and i didnt notice a huge difference to be honest).
I hold no responsibility if this tweak should cause your computer to spontaneously combust or eat your children.
Open the Registry Editor.
Navigate to "HKEY_LOCAL_MACHINESystemCurrentControlSetServicesluafv"
Double click the "start" string value, and set it to 4.
Reboot and see if you notice an improvement.