I don't think the "wobbly windows" phenomenon has anything to do with UX designers or usability testing and everything to do with developers coding the feature just because they could.
As far as new accelerated graphics capabilities enabling new UI constructs, I would say that drop shadows titlebar fading on windows are useful for subtly hinting which is the active window. A big one would be Expose-style window management which is very useful. Animations on program start/minimize and desktop change can also be useful to help leverage spatial memory which is useful to some
Many of the UI additions which are the most helpful can be the most subtle though, the flashy stuff is probably more about showing off the technology than any kind of professional UX design.