To save time, my client gave me a sketch with the idea, colors, and composition laid out. After a few questions, I was off to the races!
Evan and I wanted to have some wiggle room for slight animations. Therefore I shot everything individually and composited the image in Photoshop.
The final deliverable was a layered Photoshop file with all the elements cut out.
The layered Photoshop file allows for animations in his UI work, but also fuel to create many new images from one source file.