Its not very hard to take a few songs, that are in the same key or in a key relative to that, chop it up, little eq work, effects here and there. Not very impressing. Reminds me when I was 13 back in 1999 and I would mash up a bunch of relative samples on Acid Pro and call it my own work.
Madeon does matchups, but he's much better at it then girl talk. Check out the song pop culture.