Google saw that images take around 65% of the bytes transmitted on the web (what would a web could be without images?) and they think it's problematic to slow connection network, such in mobile network which is mostly slower than any wired connection. Therefore, an image with lower file size is a must while retaining the quality of the images itself.
After working with VP8, they have decided to release a new image format called WebP, which is a method of lossy compression that can be used on photographic images. A WebP file consists of VP8 image data, and a container based on RIFF.
So, when will this new format available to users? It depends on the browsers that will support them. Google Chrome will support it shortly (they are the official product by Google anyway). I think others will follow soon if they see that this will benefit the users (i don't see any objection of this).
For now, you can see the comparison between an original JPEG and WebP-converted image in the Gallery page.