Anecdote from watching my friends and contacts:
Since Macs went Intel, I do not know a single person who has gone from Mac to Windows. I do, however, know quite a few people who have gone from Windows to Mac.
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I switched back to the Mac about 18 months ago. Before that, Mac OS wasn't quite there for me yet.
But now, I am really happy on Mac OS and get angry when I sit down at a typical Windows machine (one that hasn't been configured by me, I mean). I don't anticipate going back to Windows unless the platform becomes better than a Mac in the future.
I used a Mac back in college because that's what our entire campus ran on. All of the early computer science classes were on the Mac, and obviously, the later ones were all on various flavors of unix. I really liked the Mac back then, but switched back to Windows in 1997 when Apple was at an all-time low (and I happened to be working there as an intern then).
Anyway... it all depends on what makes you more productive. Engineer types tend to pick platforms because one is "faster" than the other. Or, perhaps, one has a better selection of tools than does the other. I used to think like that, and was trapped by that mentality. These days, I work on the platform that makes me more productive as an artist. If I produce better work on one over the other because it makes me "feel better," then I prefer that platform.
Almost none of my artist friends use Windows (both musicians and visual artists). Macs have a reputation for being "better for graphics." I don't think this is true, and in fact, more utilities exist for Windows than they do for the Mac. But the Mac makes me feel better, and I believe that I produce better work on this platform. That's enough for me.
The default XP and Vista look is UGLY. The first thing I do when I install a new XP system is theme it so it is prettier. As a visual artist, it really bothers me when something is ugly, sort of like the way I can't stand to look at a photo with a person's head centered. I've seen photographers out there shooting away and looking at their thumbnails on a screen with a horrible desktop wallpaper on it, and that crappy default blue XP theme. I always wonder how one can be inspired when they have to stare at something so ugly while they work.
Anyway. That's my brain dump for now. Good night. 