I have been meaning to post this for a while now, so its kinda old news. The APNG format for animated PNG images is currently available in Firefox 3 alpha releases. I saw that the latest Opera 9.5 alpha releases also support APNG (look under Other Changes). I am glad to see support for the new format getting some traction.
I also came across an neat variation on Justin Dolske’s APNG image editor extension. Holger Will created an editor that uses SVG (& SMIL) to create APNG images. Updated information here. SVG paired with SMIL-based animations can produce some very good animated PNGs.