I jungle Cho sometimes. Very strong but most people won't play him because hitting the puncture can be tough, so ganks can take some effort and you aren't going to be guaranteed a kill like you would with some other champions.
This is a decent guide for it:
http://www.solomid.net/guides.php?g=2762
You might also want to watch this:
http://www.youtube.com/watch?v=eteuU7pKCMg
Cho doesn't need runes to jungle, so just try him out and see if you like him before you go and buy all the jungle runes for him.
Edit: It also looks like Riven is available on the free champion list this week, but Yorick isn't. His obscurity continues on.