Google claims that the new module can halve page load times in the worst or best case depending on your point of view. A 2x speedup is something not to be ignored and certainly not when it's free and open source.
You can see a demo in the video below:
If you have administrator access to your web server then adding a new Apache module is fairly easy. If you don't then you have to wait until your hosting service gets around to doing it. At the moment Google reports that it is working with hosting service Go Daddy to add mod_pagespeed to its 8.5 million hosted sites.
This is part of Google's "Make the Web Faster" initiative and if we all use mod_pagespeed - they probably have.