On: HTTP headers we don't want

[__jal]

I'm sorry, but that's simply not reflective of reality. There's a reason Yahoo wrote yslow.

20 bytes times billions of requests is absolutely an optimization target; in fact, this is a really easy and low-hanging one at that.

Sure, there's also a ton of garbage sites shoving piles of garbage around, but the existence of fast food doesn't mean nice restaurants don't exist.