You know what? As an MCSE, I still do not like using Vista. It is bloated beyond necessity. Granted it looks relatively pretty, but that is not a deciding factor when most people purchase an operating system. XP is, and is most likely to be, Microsoft's best offering in terms of an OS (except for DOS 6.22!!).
I have to say though, that even given my career leanings, I am an OS X convert. Apple have got THE BEST operating system out there bar none. Slick and efficient. More stable than XP sp2 as well. And that takes a bit of beating.
P.S. - Did I show up as an OS X user on the logs??
Everyone has there own preference. OS X isn't bad at all, but I still reckon Windows is the better desktop. Which is odd, as the previews of Windows 7 look a bit OS X like

As to stability, the NT kernel, and Vista kernel, do tend to be very very stable. Last kernel crash (BSOD) I had that wan't hardware related? Can't remember. Don't use Macs enough to comment on later OS X versions stability. Both OSes likely suffer instability due to 3rd party drivers rather than anything else, hardly Apple/MS fault.
If the OS + software does what you need it to do, thats all that matters

We have a few Mac users, using OS X and, believe it or not, classic OS
