Give me an example of how XP isn't functional.
And yes I'm talking about the most current Macbook Pro. My buddy work in the architecture department who all had Macbook Pros until Aug 1, and every time I was in a meeting with him he would at least 1 gray screen. And most of the time it would take him 10 - 20 minutes for it to even power back on. This was very common with the users.
Well that's just weird. Haven't heard that one before. Mine is from the previous generation, and I haven't had anywhere near such problems. In fact, I've always been pleasantly surprised that when I did have a catastrophic failure, the OS sprung back without me interfering. The darn thing fixes itself.
As for XP, NTFS is such an incredible PITA. Defragmentation is a time-consuming, annoying process that I had to do far, far too often (since I was and still do deal with large volumes of data, both small and large files). HFS+ manages things so much better by simply not fragmenting files in the first place if it can be avoided. And it's journaling surpasses NTFS by a modest degree.
XP does not have a UNIX-like permissions structure, which complicates file management between users, and makes it more difficult to manage for me as an administrator, and repair issues with read/write access. The basic folder structure is also a problem for me in Windows; having preference files, programs, and various other resources strewn everywhere down from the root directory is a nightmare when I need to fix something, because it's hard to know where to look. OS X, again with it's UNIX-like structure, makes this a heck of a lot easier by having standards. Application resources are contained in APP files, which are similarly contained in either the user's home folder under /Applications/, or the root applications directory. Preferences and other dynamic resources are held in under ~/Library/ApplicationSupport/ . Piece of cake, most of the time.
Services and the registry are flawed concepts that should be junked, the registry being the worst. An OS can survive quite well without it, and it does more harm than good.
Oh, and I don't like the taskbar and start menu.
Those are my reasons for leaving Windows, from a technical standpoint.
EDIT: Oh, and I forgot to mention, that while XP needed some amount of manual work to keep it running at peek efficiency, by cleaning caches, those preload files (have I really forgotten what they're called? Bah, you probably know what I'm talking about), and so on, OS X still uses the good ol' daily, weekly, and monthly UNIX maintenance scripts. So for someone like myself who leaves their computer on all the time, OS X largely maintains itself and is less prone to that slow but inevitable decline in speed and performance that XP so often exhibited while I was using it.