>>12
I can confirm that Firefox 3.5.5 and Opera 10.10 fully support apng. I don't know about Chrome or Safari though. It certainly is on its way towards becoming a potential replacement or significant substitute for animated gifs.
>>11
It's not a .jpg, but a gif. It's just spoofed to make it seem like such. If you go to the image properties in your browser it says that it's a gif.