I've spent today setting up a Shopify account for a client, and have had nothing but joy (another great Rails application!)
The team at Shopify created the Liquid templating language, then extracted it from the product and made it open source (hence it's used in Mephisto), but it's another fantastically easy to use "language" and has been great to me so far
When using Shopify, I've found two outstanding resources, their Wiki and the excellent Shopify Site From Scratch
My plan was to document my issues and solutions via the blog, but I've yet to come across any...