My experience in speaking French is that I've been overconditioned in favor of vous. I'm always being told to say tu by people. The most striking example to me was when I was working at a farmers' market (in the U.S.) and one of the other vendors was French. After he discovered that I speak French, he would talk to me on his breaks, I guess because he didn't get many chances to speak his language. In one of our first conversations, I asked him, "Vous habitez ici depuis longtemps?" and his answer was, "Il faut me dire tu, hein?" As this man was at least 50, and I was 23 at the time, I found it odd. The only thing I can think of is that we were both working in the same place, and maybe that made us equals.
Sometimes film throws me off too. In watching La Reine Margot, I noticed that members of the Royal Family are all saying tu to each other, and even the duchess of Nevers uses it to Margot, a queen. Is this a theatrical convention? My understanding of the French Court was that nobody said tu to anyone at all in the presence of Royalty; you even had to say vous to your own child in the presence of the king.