Saw the really cool mashup below on avc.com. I wonder what tools Kutiman used to make it.

I would love to have a desktop application geared toward making these — kind of a GarageBand for YouTube mashups. Browse YouTube, manage a library of downloaded clips, assemble them into tracks, alter pitch and speed, and spit out the final product ready for uploading to YouTube, including attribution of all the links that were used. If such an app exists I would love to know about it. Besides the technical and UI challenges, I imagine such an app might push the boundaries of YouTube's terms of usage.