I can bet I'm probably the only person on here that practices Ninjutsu. I started off just using the books and videos, but finally I turned 16, and took up a local class. It's pretty good fun, and I can definitely feel that I'm making progress. I currently hold a 9th kyu grade (equivalent to whatever is just above yellow belt i na system) It follows the Bujinkan system, which comprises of 9 different specialist schools, like muscle attacks, bone attacks, weapons, tactics, etc. I also do reading up on the side from various schools.
I'm currently working on ways to work psychological tactics into the style. I'm reading up on hypnosis, mental associations and body language and stuff like that. Good stuff, good stuff.