Sakura got her hair got a long ass time ago. Don't you remember during the Chuunin exams when Sasuke and Naruto were both unconscious? She had to deal with the three sound ninjas. She got her big moment only to be beaten retarded by zaku but she cut her hair as a symbolic gesture to show that she was going to take action in order to do something to keep up with naruto and sasuke. Scene was good but it would have been more emotional if she had done something better then just biting.