Thanks! We use WP Engine to host the site, which they have a pretty nice system set in place to host WordPress. They have a page on their system architecture here: http://wpengine.com/our-infrastructure/
Basically, it just comes down to caching in a brilliant way. But other than that, we did not do anything special to WordPress itself.
I'm assuming based on the WPMinify mention that this is a WP site - would be curious to know if the speed improvements were all in html/css/js and caching, or if there was anything done to WP as well.