SANTA CLARA, Calif. -- After his return from a five-game leave from the team -- while he received treatment for substance abuse -- pass-rusher Aldon Smith has improved substantially.Since the playoffs have begun, the third-year star has been nearly unstoppable."Teams that want to block Aldon Smith one-on-one are whistling Dixie," 49ers coach Jim Harbaugh said Wednesday. "Therefore, he's getting quite a bit of double-team chips, help from the backs and the tight ends, and he's really playing well.