I agree w/ Alcoholico and have concerns about its functioning. E.g., does it make calls to G's servers like googleapis, etc.? Anyone able to deconstruct a compiled mod?
Also, the mod does a fair amount of page code 'rewriting', something once considered absolutely not okay when browser-based because of the high likelihood it messed up your original code -- alignments changed, ditto font and image sizes, etc.*
mod_pagespeed Filter Examples [modpagespeed.com...]
*Actually, code-changing is still iffy in many quarters because it's still often wrong. Like now, with mobile translators, Or Opera. For example, Opera's "Turbo" feature (emphasis mine) "optimizes pages so they load faster on slow networks. Note that some image quality may be lost when data is compressed. ..." [opera.com...]