I cant believe someone just said only naruto and the third can use kagebunshin. Whats next, only naruto can fart since he was the only one seen farting in the story? Kage bunshins are basically fragile as previously stated, and their main purpose is like genjutsu, deceiving the opponent and supporting other offensive jutsus.

Im thinking that Naruto should have at least learned other jutsus from jiraiya, and just didnt use his brain enough to use them during the previous battles. Probably after the training kakashi has in mind, he will start pulling out new jutsus he learned from the 3 year training he did. (if the author has already thought of them after buying time with the previous arc)

About kakashis training though, the most plausible theory would be the hiraishin. I think it does fit narutos style well, since like the kagebunshin and his use of rasengan, naruto uses jutsu (used maybe...) in really creative ways. Hiraishin according to the definition stated above, seems to stretch the imagination as to how it can be used.

If it is a training that only naruto can do, it probably has something to do with using alot of chakra, since right now, the kyuubi is the only special thing naruto has going for him.

EDIT : oh and the reason kagebunshin is used very rarely by other ninjas (maybe thats why injun was not aware that jounins use it) is because it splits the chakra of the user into the number of KB he produces, obviously not a good way to save up on chakra. Naruto uses it like a crazy idiot (and he is) because of his already large chakra capacity, as well as the infinite power plant that is sealed inside him.