Mashups are labors of love usually combining two geeky things. This Dr. Who and The Big Lebowski mashup is no different. Awesome just scratches the surface on this one.
I have no idea how people even come up with the idea, much less manage to keep at it until there is a finished video. I'm sure I could probably come up with an idea.....hell I'm sure I have before, but managing to execute on an idea is what separates geeks like me from the übergeeks like Bob Mitsch (if that is his real name!)