My Dell computer is just 15 months old, plenty powerful, and came equipped with Vista Ultimate. For the first 12 moths I thought Vista was an improvement over XP, and liked it, although the improvement was not as much as hoped for, or as MS advertised. Still it was the most stable and secure system I had up to now. My previous experience was 95, ME and XP.
SP1 introduction is a major catastrophe for some Dell owners- see Dell Support Forum. Most had no problem, some had to uninstall SigmaTel drivers and install in Simple Mode, some had to go back to factory condition, and some of us tried all of the above, spent hours with Dell and Microsoft Technicians on the phone and email, and still are not able to install SP1.
A major black eye for MS and Dell in my opinion, as SP1 is supposed to be such a security improvement.
I still like Vista as a product and continue to use it, hoping for a miracle I suppose. I have good security software and practice safe surfing as best I can.