Last year Google introduced WebP, a new image format designed to replace JPEG. WebP compresses better than JPEG, according to Google's own research -- pulling half of JPEG's foundation from under its feet.
JPEG's other half is, of course, ubiquity. Every browser reads JPEGs, and hardly any browser reads WebP. This shouldn't be surprising: new standards need to do something new, not just something old, better.
On average, we get a 45% reduction in size when starting with PNGs found on the web [using the new WebP lossless mode], and a 28% reduction in size compared to PNGs that are re-compressed with pngcrush and pngout... Lossless compression of the alpha channel [in WebP] adds just 22% bytes over lossy (quality 90) WebP encoding.
This means that WebP now does lots of stuff that JPEG doesn't -- and also does most stuff that PNG already does. So Google is now poised to present WebP as the best of both (old and new) image-format worlds.
WebP is unlikely to cause any huge waves any time soon. (As far as I can tell, it doesn't change anything radically.) But new image formats have been due for some time, and maybe WebP is the wave of the future.