Persistent cart is an interesting concept: On one hand I like the idea of a session that expires with the device I am using. On the other I see why merchants may want a cart that acts more like a saved wishlist.
If you're someone that has a Shopify site but runs an offsite blog (like wordpress) you'll probably want to be able to show the cart contents on that blog. The usual AJAX API calls won't work since you'll hit CORS errors but JSONP comes to the rescue.
If you have multiple domains attached to your Shopify store you might want to detect what one is currently being used. You might need this is if you want to show certain content if the Australian domain is used versus when the American domain is used.
Shopify Scripts is a great (and fun) feature available for Shopify Plus merchants. There's lots of interesting things you can do with Scripts, with one being the ability to remove a discount code from the cart automatically.
Freakdesign has worked with some pretty cool clients (some noted below) - all different sizes and sectors. From Brisbane, Sydney, Melbourne through to worldwide, there's few places our work hasn't been. Even the work has been varied with Shopify designs, EDMs, Branding, Illustration and everything in-between. Nice to have variety!