i dont think naruto knoes the full capacities of the rasengan...because when he used it in kabuto he went flying away but he was already healing himself before the initial impact...and when he sees jiraiya use it it was just to push the guy outta the way and knock him out (or not)...other wise he as just seen it used on inanimate objects, eg trees...i dont think he realises that it would rip you to shreds if used properly..

im thinking the first time he [naruto] kills someone it is going to be with the rasengan and it aint gunna be pretty..