I used FB connect to sign up way back when and I followed my friends. Some of my friends in UI design started pinning cool stuff, so I followed the original "pinner." Then I started following Pinterest's suggestions for me.
Recollecting this makes me realize what a great product is -- it just evolves with you. It couldn't be simpler.
You have a lot of ways to discover UI design on Pinterest (if you look at my profile – pinterest.com/xethorn – I mostly use it for that particular reason and architecture work.)
Things you can do to find UI work: you can either follow the boards of people who are relevant to the field, you can also browse what's happening on specific domains ("More from [url]" in the sidebar of the closeup) or you can simply browse the related interests.
