Crumpet: You’re right, this is a debate that’s been going on for 25 years that I know of. I honestly don’t remember which way was up in the first 3D application I used (text-based) but the ones I’ve used most before Blender (Sculpt-Animate 4D, Alias Animator and Maya) are the ones I got used to, so Z-up seems natural to me.
I came into computer graphics as an artist and my first introduction to Cartesian coordinates in art was on a computer with Y-up. It felt right since that was the way I learned it in math classes so long ago. Extending things into a 3rd dimension with the Y-axis still pointing up felt right, too.
Don’t get me wrong; I’ve adapted to Blender’s (and 3DS Max’s) way of doing things over the past couple of years. It still feels weird if I stop and think about it, but mostly I can ignore it and just get on with the creative process. And I also realize that if Blender suddenly changed to a Y-up system, I like wouldn’t feel any more at home than anyone else; I’d have to re-adapt, too.
There is one part of Blender, however, that still seems more at home in a Y-up system, though. Armatures. Interesting, eh? Ever notice how, when it comes to orienting Custom Bone Shapes to a rig, even those who make video tutorials sometimes get confused?
xrg: I didn’t mean to imply that Ctrl-Shift-Z is unusual in 3D. Every 3D application I’ve used over the last 25 years has used it for redo, those that had it. The 2D applications have been split roughly 75-25 between Ctrl-Y and Ctrl-Shift-Z. My intention was to bring up the confusion of shifting from 2D to 3D where both the keyboard shortcuts for redo and the direction of the Y-axis change.
To sum up: I’m very grateful for Blender, The GIMP and Inkscape. Sure, not everything is the way I’d like them to be, but I’d like to have a bigger apartment, more money, be taller and have more hair, too. 
Not to mention, about 25 years younger.
