My son-in-law just got back from a business trip to Tokyo and said he has never seen a cleaner city in his life...
He said that if someone dropped a cigarette (most Japanese smoke, he says) on the ground, it wouldn't be there more than a minute before someone swept it up....
I've only seen Tokyo once. My memory of it (from a 15-y/o point of view) was that it was incredibly crowded.