So far Sasuke has had three chances to kill Naruto. The first came when he plunged his chidori into his shoulder (though he says he was aiming for a vital point and Naruto had used chakra to redirect it at the last moment), but the Kyuubi interrupted that when he started feeding Naruto power.
The second chance came after that titanic fight. Sasuke seemed to be in a lot of pain, but Naruto was completely unconscious. There Sasuke chose to let Naruto live because he didnt want to achieve power the way his brother did out of spite. As he claims.
The most recent was when Naruto, Sai, and Sakura had tracked him down after the three year jump. Sasuke had Naruto pegged, guard down with no defense, his sword about slip into his side when Sai (It was Sai right? I know that ANBU subsitute squad leader tried to stop his sword also... cant remember who did it first) got in the way which woke Naruto up out of his wierd trance...
Question is, do you think Sasuke had/ has it in him to really kill Naruto? Do you think he's crossed over that far to take the life of a friend that considers him to be as close as family?