Interesting, and good to know that the "tu" form is used over Internet forums. Not having interacted on a French forum, I assumed one would use "vous" automatically. I also didn't know that it was normal for younger adults to use "tu" right of the bat, since, not being an adult myself, I usually use "vous" with adults and expect them to use "tu".

The situation is further complicated by the tutoiment/vouvoiment varying with dialect. In Québec, for instance, "tu" is used more frequently with teachers than in France, and I've never heard a teacher address a student with "vous."