I am one of those people who can't stand it when little kids call an adult by his or her given (first/Christian) name. I think it is rude and inappropriately familiar. I think that it shows a lack of respect.
So, I usually get around this at home by having my kids call adults in their personal life “Aunty X” or “Uncle Y” despite a lack of the proper relationship. At daycare, Big Boy called the workers “Miss.”
It is different here in Scotland because we live in an international community. Many of our friends are American, specifically from Houston. They do not call non-related adults “Aunt” or “Uncle,” they use the term “Mister” or “Miss.”
So, since we have moved here we have adopted these monikers as well. I really don’t love them, and when we go back home we will change back. It does feel very "Dallas" to use those terms....