This is a Theory.<u>Theory</u>

After a ninja uses a move consistantly and the move is pretty simple, they dont need to use hand seals.

Its shown in the way kakashi can do kawarmi(sp?) the replacement jutsu without doing hand seals. He never does them, where as sakura has to do numerous hand seals in the forest(2nd test in chuunin exam)

Also kakashi doesn't have to use seals to do clones(water/kage/other). This is shown when he fights zanza, when he fights itachi. Granted he does do one seal when he is on the bridge after zanza lost the capability to fight and they were scaring the mob, but he doesn't do nearly as many hand seals as naruto does when he does kage bunshin.

Sasuke when he first uses the Chidori against Gaara, he uses numerous hand seals. However when he fight itachi, he doesn't use any hand seals. Also kakashi doesn't use any hand seals when he does chidori.

Itachi - doesn't show any hand seals.

Orochimaru - Hardly ever uses hand seals, but can do the mud clone thing, the turn into a shadow, numerous other things without hand seals.

So my theory is that after gaining a certain amount of experiance in using a jutsu, you no longer need to actually form the serperate hand seals. Of course it would be easier to learn the simple jutsus than hard ones.(kawarmi vs. kage bunshin)

What do u guys think?