What about Windows Vista? I know it's one of Microsoft's larger mistakes, but some people actually use it.
IMO as far as Microsoft's list of mistakes goes, Vista doesn't make the list, certainly not for technical factors. We have Bob, MS Binder, probably Project, that was sorta weird; some might consider win32s to be a mistake, WinG was a dead-end, ME is better than 98SE in many ways, it's problems were mostly inherited from the 9x architecture and weren't unique to ME (except that stupid "no DOS Mode for u" stuff).
ST's post highlights the reasons why I hadn't replied. the Poll options are so limited as to be silly. It's like asking "What kind of pop/soda do you like, Pepsi or Coke?".
Well that and I'm in the middle of a debate between myself and a member on another forum about UX design; my stance being that all OS's have critical problems in the area of UX design; some have gotten worse, others have gotten better, but overall, they all suck, and trying to pretend otherwise for any OS is silly. Their argument is that all User Interfaces not designed by Apple suck, and they back this argument up by questioning my parentage, which was a odd way to debate. And when I noted that colour-coding caption buttons is pretty silly, since red yellow and green do not accurately portray close, restore, and maximize, and it is also culturally biassed since colours mean different things in different locale's. Their argument against that pretty much boiled down to "only the U.S matters" which was pretty much where I gave up on the poor fellow.
Since I'm here though better respond to the topic: I use Win7 on my desktop and Mint 13 on my laptop. Neither are set-up for dual boot; laptop used to be mint 10 and Win7 in dual boot until the drive failed and I installed Mint 12 on spare drive, which consequently failed a few weeks ago and I managed to salvage it and get Mint 13 on it. (It's a stopgap measure, I don't have anything important on the drive because it will fail soon enough).
My older laptop is running Windows98SE, I'll power that on every month or so just to make sure it hasn't died.