I've been doing theater for the past 7 years or so, and I think I can honestly say that I don't get nervous at all anymore. Excited, yes, but not nervous. The strangest thing, though, is that more than likely, as I'm waiting in the wings, you'll catch me yawning. I don't know exactly why that is...it's not like I'm tired or anything. But I yawn a lot. I'm weird like that, I guess.
That's a big contrast to when I had my first leading role in high school. I was playing a melodramatic painter-type dude, and I had this really super-de-duper melodramatic entrance. Anyhoo...as I jumped out onto the stage and go all out with my little monologue, I noticed that my right leg was shaking uncontrollably. I had to concentrate really really hard on it through the opening scene to get it to stop. Looking back, it was rather humorous. I don't think anyone in the audience knew, but I sure as hell did!