I am 44 and my only child is merely three years old, so I am on the bandwagon of using Mr., Mrs., Miss, Ms, etc. with the LAST name of the people.
Calling people Miss Jen or Mr. Peter is something that my experience has taught me is reserved for people who are related, such as family matriarchs or patriarchs, or hold a very high status in your inner circle, such as honest-to-goodness lifelong friends.
My son calls my siblings and my in-laws Aunt or Uncle So-n-so.
There are no friends to whom he refers as aunt or uncle.
My father's wife is called Miss Kay, and my long-time friend (since we were about 6 months old!) is also called Miss Brenda. My mother's husband is called, simply, Robert, as that is what my boy started calling him when he learned to speak.
That said, my son calls my best friend by her first name because he is best buddies with her son, spends a lot of time with her and she is his "grown-up" friend. At this point, she and her husband are the only adults whom he calls by their first names. The parents of his other friends are called Mr. and Mrs. last name.
Even at 44, there are STILL people whom I address as Mr. and Mrs. A life long family friend (my parents' age) signs all her correspondence to me as Anne, but I still call her Mrs. Orman. I just can't call her by her first name. Same happened with one of my junior high school teachers with whom I chat on Facebook. He said to call him Doug, and, again, I cannot bring myself to do it.
Unfortunately, the school my boy attends uses the "Miss first name" approach. I tried, unsuccessfully, to encourage the school to go to the formal Miss last name. I believe that the way a child addresses an adult can set the tone for all of their interactions with that adult. And it carries over to other relationships. I think that the loss of demanded respect in how children address adults has contributed to the break down of civility in our society, and I would be ever so happy to see the return to formal address.
I'll be interested to see other responses. Thanks for the great question.