Windows XP Professional at work - we do a lot of development work here and XP Pro is the standard operating system used by the company, so I can't argue too much - although I also use a Mac in the office because we do cross-development work and we have that one around for testing purposes.
Install size: 2.83GB
Windows XP Professional at home - but a special "homebrew" version that I optimized exclusively for gaming.
Install size: 480MB
The one on my home computer literally flies. It uses only 40MB of my 2GB RAM, and starts with only 23 processes. Virtually everything that is not gaming-related is stripped from the OS.
Why do I use it? Well, a few thousand DOS/Windows games in your collection will keep you using Microsoft!
I will only upgrade to Vista once DirectX10 games are out aplenty and there are more than three flavors of DX10 graphics to choose from (and no, those newer craptastic 8500s and 2400s don't fit the bill).
If there is another OS that can run the entire vast library of Wintel games natively (or emulated but without suffering performance impacts) then I'll consider. Otherwise, for PC gamers, I don't see how you can go wrong with XP today.
