Since I do SEO and have a client on Shopify, I decided to use it for myself as it will give me a bit of a playground. I've been providing the same service for a long time but have recently productized it so it is more quantifiable for customers.
Anyway, I just got my first order! The site is very new (only 16 days) and obviously not much traffic yet.
For those who are interested this is the site - it is super simple, using a free theme for which I customized a bit of the code and using the Custom Product Options app to add the per-product custom input.
If you have any constructive feedback, I'd love to hear it.
So it seems your focus is SEO service and not actually eCommerce/Product Catalog.. In some sense, I am in same boat. My focus is RoboNegotiator.com service and to make a point, I am building my dropship store where buyers can negotiate with me (seller) through my RoboNegotiator button. SEO and many things (including content) needs to be built though.. In early phase.