The Core

Interesting, how do you feel about giving them that much control?  any potential for automated snafus?

implements all the elements evaluated in the PageSpeed browser extension

I have to check details with my webmaster and I haven't looked into exactly what the Apache mod does but he intentionally chose not to integrate all the PageSpeed suggestions such as:

1 - "Serve the following static resources from a domain that doesn't set cookies"
2 - "Combine images into CSS spirtes" (we didn't want to do this with every image - understand the Apache tool couldn't do this)
3 - "Combine external java script"
4 - "Minify CSS"
5 - "Use efficient CSS selectors"

There were (apparently) good reasons not to implement the PageSpeed suggestions to the letter.

if you think your time is spent better else where

That was part of it (negligible benefit to time spent) and also the cookie thing.  Our CMS sets cookies for its own tracking purposes along with other third party scripts/ad services.

CSS sprites, I am told, are problematic if your images are changing frequently within the sprite set (graphical features that change/automated according to various rules like sales/popularity etc.)

Again, there may have been other reasons as well, I don't handle it.

I have begun testing mod_pagespeed.

First thing to notice is the filename of RPM mod-pagespeed-beta_current_i386.rpm

Beta? No where on the Page Speed project site does it say anything about beta. I'm aware of that G likes to keep stuff in beta for as long as possible for legal reasons, but seriously guys? Don't lure webmasters in to installing beta software on production servers. 

I suppose you could "cloak" for cookies, ie not set them if they the UA is G :-)