In my house, there are 8 PC's. Each PC runs a Windows OS, though 4 of mine also run Linux (Ubuntu).
Windows Vista ----------------- 2 PC's --------- 25%
Windows XP Home ------------- 3 PC's --------- 37.5%
Windows 98 SE ---------------- 1 PC ---------- 12.5%
Windows 95 ------------------- 2 PC's --------- 25%
Ubuntu 8.04 Linux ------------- 4 PC's ---------- 50%
My percentages are way different lol, Linux only wins because it's dual-booted with another OS. The only reason I'm using old Windows versions is I have a few old Pentium machines that can't run anything better.
As for Vista, it is a nightmare on my parents' computer (which they got a month or so after Vista's release). It wouldn't even update to SP1 properly and has tons of problems.
However, my new HP laptop also runs Vista, and it is very smooth, just as good as XP except for the issue with unsigned drivers (can't overclock my video card, makes me ANGRY)...just hoping that someone finds a way through this failure of Microsoft and lets us use ATiTool or RivaTuner drivers on Vista x64.