See: http://blogs.testbit.eu/timj/2005/08/06/06082005/ (page moved)
I just implemented the PNG image loader for rapicorn, albeit without animations so far. Regarding the Animated PNG specification, i actually got word from Stuart Parmenter in response to my recent blog entry, that the spec should be fixed up and finalized in the near future. So there’s still hope for a low-complexity animation format.