This seems like a really basic question that has been surprisingly hard to find an answer to.
CABasicAnimations set up with "affineTransform" as the keypath haven't worked for me, and in a bunch of places I've seen people eventually resorting to use CATransform3D instead with the "transform" keypath. Sure that's a hint, but it would be good to have confirmation if "affineTransform" is meant to work or not?
Technically, affineTransform is not a property of CALayer, and is documented as a "convenience method" wrapper around the transform property, which is documented as animatable.
It's only really by objective-c's implicit conversion of keypaths to selectors that it appears affineTransform behaves like a property when use (under most circumstances) in a keypath. However, the CA libraries are setup to observe only certain keypaths, and that's not one of them :-)
