Google’s mod_pagespeed does a great job at optimising web resources such as HTML, JS, CSS and even images.
I use it on a lot of customer production sites as a great partner to APC cache for super fast web sites.
I won’t go into details on how it works, if you’re reading this, you already know!
mod_pagespeed caches resources to disk. If you are running on a heavily loaded server or a VPS, disk IO is a premium.
So we should really cache to memory, its faster, cheaper and easy to set up.