Hey, pretty spiffy. Good to have a reference for examples specific to comic use. I would make a couple of technical notes about your guide though, so please don't take offense.
GIF... you should really point out that GIFs are technically lossless. The reason they don't look like the original image though is that they're limited to 256 colors. But you can cut and paste pieces around a gif image all day, and save again and again (as long as you're not adding/changing colors), and it doesn't lose more quality (unlike JPEGs) It's the color loss/limit that makes them so ugly, but for black and white (or grey) 256 shades of grey is plenty. The weird pixelated effect you get in GIFs is called "dithering" and it's when a program tries to fill in intermediate colors. E.g. trying to make a shade of blue-green by putting a green pixel next to a blue one. I always hated it, so I either manually reduce my images to 256 colors when I'm making them, or opt for PNG or JPG.
PNG is lossless, and as such, there's no reason you should really ever use less than the maximum compression. The visual result will always be identical. The higher compression only uses up more CPU to display it. That was a problem on 486 PCs when PNG was first introduced, but not on modern machines. Part of what makes PNG so useful is that you can't go wrong with it. Just set maximum compression and your image will look perfect every time. PNG also supports true transparency, so stuff on a page can blend with the background. That's really not useful for comics, but comes in handy for other web design. The xepher.net logo on the main page is an excellent example, as (in firefox or other good browsers at least) you can see how the shadows blend perfectly as you scroll.
PNG actually supports different color depths too, so you can set it to 256 colors just like GIF images are, and get equally small file sizes (with ugly, dithered colors too.) PNG also has a lot of other options that most people won't need, like interlacing, and different compression algorithms. BTW, your example PNG page links the level 6 image for both level 6 and level 9 examples.