I installed it on 4 different machines. The slowest was 33 minutes. The fastest, (my own Core 2 Duo machine) took less than 25 minutes.
All systems are running smoothly. All devices and their associated drivers work as they should. Two of the systems act as Media Centers and perform their function extremely well. The other two, my main system and my wife's home business system actually work better then when XP was installed on them.
The printer and scanner drivers were native to Vista and installed as soon as I plugged them in to USB ports.
All-in-all I'd have to say it's been a very pleasant experience.

BTW, one of the installations was done using the Upgrade version of Vista Ultimate. The installation was easy. Yes, I had to have XP installed, which I did, and I had to initiate the Vista installation from within XP, but it was possible to do a clean installation. When prompted I simply selected the alternate installation option and then selected a clean install. Vista put everything from the XP partition into a folder called Windows.old and then installed the new OS to the remaining empty space on the partition. When the installation was finished I simply found the Windows.old folder and deleted it. Voila! New OS. Clean install. No remnants of the old OS.