I was interviewed by a company a while back. They were interesting nice people and It was kind of a fun process. They gave me this test:
Select a piece of software you use on a daily basis (Gmail, Twitter, etc.) and find a part of the interface you think could use the most improvement. Take a screenshot of the current UI, explain what you dislike about it, and suggest improvements. Illustrate your improvements with a mockup, wireframe, or drawing.
I opted to work on the current Facebook experience. My ideas can be viewed by clicking the image below. You can also download a pdf version by pasting this link into your browser: