Sounds fun, I wish my school did that! Haha. My first mosh pit was at a Slipknot concert, I got pushed into a circle pit, it was fun..and I only escaped with a few bruises and a bloody nose. =)
My first mosh pit was at a Lamb Of God concert. I didn't know who they were; my friend wanted me to go with her, so I went. I broke my arm and got trampled. I was bleeding. Everyone else around me was, too. She had a panic attack so we had to leave.
It was the most painful experience of my life. Good concert, though.
Eh, I've been told that mosh pits are scary, but when you're in there bumping the crud out of everyone and not just standing there, it's pretty awesome. Until you fall and get trampled on, of course. :/