re: Sir and Ma'am..... Do you use it?

Yes, I generally say it towards people with whom I'm not very familiar. This includes people that work at Walmart or McDonald's or wherever. To me, I hope it conveys the idea that I respect them and that I don't think I'm better than them.

However, I don't say it to people that I work with, even if it's a superior or a client because it makes you sound like a kiss-arse. If I don't call everyone sir, I'm certainly not calling the boss by it because it would be pretty transparent.

ETA: The people knocking the practice for sounding antiquated or attributing it to some ridiculous class structure are just rationalizing their own lack of courtesy and respect.