I've been playing with Mod Pagespeed at work quite a bit recently, we don't do Drupal hosting as such, but we set up infrastructure and make sure it's working for a number of our customers.
We've previously had to work in an envionrment where Mod Pagespeed was used very aggressively, and broke various pieces on the sites, this was not fun.
When implementing it on our sites and servers, I wanted a much lighter touch. Pagespeed should make things faster, and shouldn't make development slower.
Complicating matters was that we light to run our sites behind Varnish, the amazing HTTP accelerator. If you follow the default pagespeed setup guide for reverse proxies, then you end up disabling a lot of caching in Varnish.
After quite a bit of experimentation I've settled on the following base config for mod pagespeed:
This is a fairly conservative set of config, that makes some simple optimisations to CSS, JS and images, but without busting the Varnish cache.
So, you get the super serving speed of Varnish combined with the lovely optmisations from Mod Pagespeed, and no page breakage that we've noticed :)