Google is failing me somewhat on this (I think because the terminology for PolyFill/Shim/Spackle is new and diverse at the moment). I'm trying to find a good JavaScript PolyFill or Shim for webkit's (and now as of the RC FireFox 4's) CSS transitions.
I have found this work that Weston Ruter did, but it hasn't been updated in a while, and uses browser detection as opposed to feature detection.
I also uncovered FakeSmile but it is geared mostly to SVG animation.
Does anyone know of any good libraries to fill in this functionality? Preferably something that would work with Modernizr and is still being actively worked on. So far the best option looks like starting with what Weston came up with.
There is a very good CSS3 transition polyfill for jQuery called jQuery.transition.
You can just use the usual animate() method in jQuery, and it will automatically use CSS3 transitions if available, and if not, it will fall back to vanilla jQuery.