I remember reading about this while it was in development and now they have revealed the finished product at a TED 2013 conference.
Using your device’s camera, 3Dfit creates a 3D model of your face. The model is paired with scans of 2,000+ frames in the glasses.com inventory, creating an interactive photorealistic image. Unlike anything I've seen, with 3Dfit you can then try on and view frames from any angle — perfectly scaled to your face.
I was pretty impressed with how well it worked. You really have to see it to believe it. Even if you don't wear glasses, it's a great way to try out some new sunglasses!
The app is free, but only available on iPad 2 or better. Just do a search in the app store for glasses.com