I find it really interesting how expensive it is to have <img> tags without specifying a width/height. I always knew this was best practice, then stopped doing it once I started experimenting with "responsive web design."
You probably know this but you can just specify something like "height: auto; max-width: 100%;" within a media query if you have an image that's supposed to at most fill the full column width. That would then override the inline height and width attributes.
This is interesting, and I hadn't heard about it until now. Would you care to elaborate, or point to further information?