I have just clean installed the final version of Windows vista few hours ago. The installation process took only 30 minutes! That was fast, compared to previous versions of Windows.
However, when I installed Windows Vista (RC1) for the first time. It took around 2-2.5 hours for the installation process to finish. I was using the "Upgrade" option at that time to upgrade from my Windows XP SP2.
So for those who are planning to upgrade to Windows Vista, my suggestion is to do the clean install instead of upgrade from previous version. Addition to the shorter setup time, I think clean installation gives the system more stabilities too.