For this tutorial the biggest challenge was finding the bird that the tutorial asked for, and making it black, as the only colours I could find it in was blue. I ended up having to use photoshop to change the colour, and the last step, which was to give the bird a faint poka-dot layer, wasn't accomplished because it wouldn't work on the computer. The biggest success I think was creating all the different shadows and highlights for the main shape of the icon. The most useful thing that I learned while using this tutorial was how to duplicate an object, and how to make things transparent.
http://bloomwebdesign.net/2012/04/create-a-professional-3d-twitter-icon-in-illustrator/
http://bloomwebdesign.net/2012/04/create-a-professional-3d-twitter-icon-in-illustrator/