UX and UI often go hand-in-hand, because <i>(wait for it)</i>.... The UI can greatly effect the UX. As a developer, I usually just pay attention to the UX. I am always on the look out for how the user is going to be using a product, interacting with it, and ultimately, how to increase customer satisfaction. The UI is often times, a driving force behind these concepts.. But yes, they are very different subjects, and technically, the UX can be awesome even when the UI looks like shit.