PNG is a pretty versatile format. If you are going to use 900K images in headers and such (like http://eyewire.org/wp-content/uploads/2012/01/11.png in http://eyewire.org/instructions/), it would be nice if you could use interlacing so those of us with slower connections can get the gist of the image instead of having to wait a dozen seconds.
The alternative would be actually shrinking the images to the size you are going to use them beforehand, but that’s more work.
Thanks for pointing that out octayn! I hadn’t heard of that, we’ll look into it. One of the things on our list is speeding up some of the static content, and to be honest, we can probably convey the same message with fewer images on that page. This may also be another way to speed things up.