Why Great Designers Steal—and Are Proud of It

http://cameronmoll.com/archives/000016.html

Cameron Moll calls it "nodes of inspiration" and this was highly influential on my budding young design career at the time. In essence, never rip off one interface entirely, instead you should rip off many elements from different sources and put them together in a seamless way.

It's a good way to build up the skills to make your own stuff from scratch and is the design equivalent of studying someone else's code.