Up front: I'm an advocate of 3D for usability. Much of it is glitz, which *can* enhance the user experience, but it also opens the door for new types of visualization that can provide novel ways of usefully viewing/using information not possible with static perspective 2D (a coined term representing classic Win95-esque desktops).

Take a look at this (specifically the first half). It's a good example of what is possible with acceleration mixed with cleverness.
http://www.ted.com/index.php/talks/b...hotosynth.html

Sure this can be done in 2D, but I'm guessing that it would more easily and efficiently be accomplished with 3D hardware; not to mention kinder on the battery of certain tablets.

Even glitzy compositing windowing systems like compiz fusion receive usability benefits from acceleration.
1) Zoom out to see all windows
2) Zoom in to magnify
3) True transparency of varying opacity
4) Quick tiling of windows for application selection.
5) Increased UI responsiveness

}:^)~
YARR!

Caaaaap