We've recently had the pleasure of doing some unique customization of Shopify and were ecstatic to work with the platform again.  After working out some recent headaches on some poorly designed and documented Movable Type plugins (Facebook Connect - built by the MT team), it was a pleasure to work with Shopify.

We needed to create linked products to allow customers to buy a bikini top and bottom from the same page.  This currently isn't allowed as out of the box functionality from Shopify, however working with Shopify's easy to understand, easy to work with liquid code allowed us to quickly add this functionality.

We're quite fond of Shopify's liquid code, API library and easy to modify themes.