One other thing that Shopify did well was extract a lot of code into open source projects. Liquid, DelayedJob and ActiveMerchant are all thanks to their hard work.
So rather than just make money for themseves (which they did do), they "moved the ball forward".
When I first saw Shopify I thought "That's never going to be successful". I immediately ruled it out and how wrong I've been proved! What they did, as I've watched them grow, is to launch early and then progressively make their application better and better. That is something I've read and read countless times and watching it in action has been inspiring and sobering (in that I'd not done that with my own products). I'm really pleased for them and wish them a lot of success. It has also inspired me for our new products and we soft-launched one within a month from a standing start.
After wanting to just create a simple online store and initially setting up Drupal and Magento, I've found Shopify to be surprisingly customisable and easy to use. Really impressed with their product. Love the start-up story also. I can see how Tobi came to the conclusion that the stuff out there for the non-corporate market wasn't that great (even now).