Parts of Magnatune are very image heavy, such as those that show many album covers or many artists.
Starting today, if your browser supports it, these images are in Google's new WebP format, which (in my tests) results in images about 1/2 the size as JPG, without the annoying boxy artifacts (especially around edges and text) that jpeg often creates.
I recently added "retina image" support widely to Magnatune, so that if you have a "retina monitor" (iPad, high res Android, or 4k resolution monitor) the Magnatune web site automatically detects this and sends you album art and artist photos at twice the horizontal and vertical resolution. The downside to this is that the "retina" images are much larger, which is why I wanted to implement Webp support.
In my tests, the Webp "retina" images are 25% smaller than the equivalent non-retina JPEG images.
Currently, WebP is only supported in Google-based browsers (Chrome on Desktops, and Android) as well as Opera.
Hopefully WebKit (Apple) and Firefox will eventually support WebP. It seems very high performing.