Google has made the case recently that WebP is ready for the big time. In fact, it has converted all of the graphics in the Chrome Web Store, to save bandwidth and improve page loading speed, but also to showcase that the new image format can be used by major websites.
Google itself uses it, though the fact that it's only supported by Chrome and Opera limits its reach.
Interestingly enough, Google seems to be ready for the day when WebP support will be ubiquitous.
In fact, its photo storage service, used by Google+, Picasa and even Blogger, can easily serve any photo as WebP, as discovered by the Google Operating System blog.
Images stored by Google aren't served in WebP by default, but you can get the WebP version easily, all you have to do is modify the URL of the source image a bit.
Google's image converter will provide you with the WebP version of the image, which can be significantly smaller, even half the size for comparable quality.
Of course, the image will only be displayed in browsers that support the format, in Firefox you'll be asked to download it.
Normally, the URL for an image hosted by Google looks like this:
The interesting part is s900 or sXXXX for a generic photo – that code represents the size of the image displayed, in this case 900 pixels on the largest side.
The code can be replaced with others, to generate a specific width or height. Instead of 's' use 'w' for width and 'h' for height. You can even combine them like so w500-h300.
But this code can also be used to generate WebP images, simply add -rw to the end, for example s900-rw.