I've played Nocturne a bit and he is really fun. I bought him when he was on sale a while back and I thought he was worth it.
I've played him bot and recently tried jungling with him. If you've played Garren, use a similar tactic. Hide in the bush and then ambush! I've watched a lot of amaizing ganks on youtube and I find it a useful tactic for when you use your ult to jump them, I prefer to when they are under a tower..all alone..and ult jump them and instantly use my fear teather, and use my q to just lay down the dmg wherever they decide to run to. Me and the tower double team him/her. Take that dunkmaster yi!
He's fun, but does indeed have a learning curve. Also he has a really stunning jungle clear <3