As for "many people," I would use this as a vague limiter, as in "many people prefer to get their news via Facebook." On the other hand, I would describe a group of people that I saw in other ways: "there were a lot of people at the mall today," or "there were a whold bunch of new students in my night class."

You have asked some tricky questions here. Ma'am or Sir is okay, as is Miss if it is a younger woman. But here in California, many people do not like being called by these formal titles, so I often just say "Excuse me, ..." or "Hi, ..." and go on with what I want to say.

Hello. :) I agree with Thomas Gault. If you're on the phone, at the store, at the bank, working (with customers), talking with a stranger on the street, etc., then it would be perfectly fine if you referred to them as 'Sir' or 'Ma'am/Miss'. Also, it never hurts to be more polite than not polite at all. :) So, yes, those three are very polite. Also, like Thomas said, you don't need to say Sir/ma'am/miss. Saying "Excuse me/pardon me", etc. would be fine as well. If you're still not sure, just at least greet them or say "excuse me" and then continue with what you need to say. :) Examples: Excuse me, Sir, how do I get from "here" to "here"? Hello, may I get an order of Phad Thai? *You're on the phone with a bank assistant: Excuse me (Miss/ma'am), are you still there? However, if you're talking with your friends about a person you're not too familiar with, then you could refer to them as guy/man or lady/woman or girl (if she is about a teenager or younger). Examples: The guy on the phone said that he could help us. ^___^ That lady thought I was someone famous. ;) Let me know if you have any questions/concerns. :)

I got a feeling that in some occasions, the store clerks use 'Ma'am' or 'Sir' in the pretense of doing his job as a store clerk who simultaneously wants to chat with his while ringing up my purchase in order not to appear rude. I live in New York.