First and most importantly lets highlight an exceptionally important issue that well equipped web developers _always_ seem to forget: 2.X was 84% of Android market share as recently as a month ago. ICS and Jellybean are tiny by comparison.
Leaving that aside, Android's stock browser and Chrome still has serious issues with CSS based transformations and animations on non-trivial pages which mobile safari has handled with aplomb for the last 2 _major_ versions. This is not ICS, I'm talking about Jelly Bean. Even the newest flagship devices from HTC, the One X, can barely handle complex content animations. Again, toy examples have worked for a very long time but anything exceeding the compositing engines tile size just falls over completely.
Unrelated to animations, here's a bug that I logged myself against 4.0:
http://code.google.com/p/android/issues/detail?id=27959&...
Wherein a full width position fixed element fails to reflow on orientation change.
https://github.com/scottjehl/Device-Bugs/issues
If you look at the issues we've recorded over time you'll see there are plenty of iOS issues there too, but the degree of pain caused by them is vanishingly small when weighed against those we've dealt with from Android.