Most of this is pretty standard scaling advice - except the "Tobi" caching, which has some good ideas I haven't seen elsewhere.

DHH describes a similar caching scheme here:

http://37signals.com/svn/posts/3113-how-key-based-cache-expi...

Im surprised how transparent this is. Halfing response time on a system that large is no easy task.

What is there system written in? just curious

Shopify itself is written in Ruby using the Rails framework. I believe we're one of the oldest and largest Rails projects out there.

Some parts of our infrastructure are written in other frameworks (e.g. Thin) and languages (e.g. Go).