Before and after

Really impressive: how a proper setup can really help you get the most juice out of a slice!

CPU graph I/O graph

Before: Apache, with as much caching code as possible enabled (e.g. WP Super Cache)

After: Nginx, explicit cache directives for static files so they are cached for longer, proper logrotate settings, plus APC cache (just in case there was something else left to optimise!)

NOTE: both graphs don't drop almost to zero at the same time because I didn't fix everything the same day.