Having read your extensive and very helpful guidelines on load-time optimization, there is one thing I found notably absent. Many graphics programs export RGB-alpha PNG files by default. Since many of us still avoid alpha transparency in PNG's like the plague due to improper rendering in IE6, I think you'd find a vast majority of PNG's on sites out there do not need their alpha channels at all. Your advice on using pngcrush for optimization was somewhat helpful, but by far the best optimization I get with PNG's is to remove the redundant alpha channel - saving a much larger percentage of the file size than any of the other optimizations you recommended. Obviously this technique is not an option whenever transparency is desired, but in my designs at least, this is a rare thing.
Am I missing something here, or was this a notable oversight on your part?