Where an image has a width imposed but no height, the image display does not maintain the aspect ratio of the image's actual size. Also, where there is a max-width set at 100%, an image does not respect that when the parent is less than that. I put a test case together at the URL above, other browsers (IE7, Opera & Gecko) seem to behave the same (and in the way I'd expected).
Alastair, have you tested this in the nightly?
Hmm, I had, but re-opening the test case with it looks fine. Does the webkit rendering not come through if you already have Safari open? My apologies, I had lots of browsers open at the time :-/