I use WebP on linux-tips.us. Well, I don't really do anything - there's a plugin that does all the work for me. It's supposed to generate WebP images automatically, though I am just now realizing that I've never tested it.
If something better comes along, and the transition can be done smoothly, I'll move to that - after it has matured a bit.
Thanks for the news. I had no idea about this file format. I'll have to do some experimentation on some high-quality pictures from the camera. Those are huge in RAW format and make giant jpeg files. They're like 5 or 6 MB from a 36 mp DSLR.