The website's founder Matt Kohr, now a freelance concept artist, creates these excellent video tutorials which can all be accessed FOR FREE.
One of his videos focuses on silhouette iteration, and today I've basically been doing the tutorial. The videos are really easy to follow and he goes into just the right amount of detail that it just sticks.
Anyway, I'd highly recommend giving his website a visit if you would like to improve your 2D skills.
So the tutorial basically allows you to experiment with the inner detail to silhouettes using masks in photoshop. I created a silhouette which I liked, made several copies, and made the inner detail different each time to suggest different results from the same silhouette. Rather fascinating.
Anyway here's his example.