I've seen both TPM and AOTC in it's midnight pre-opening days (before you guys did, because of the time zone!), and in both the reactions were something like that, because the theater was full of SW fans and geeks, no "normal" person. In TPM I remember people booing when "A long time ago" appeared onscreen because Lucasarts translated it, people going "yay" when the Star Wars logo appears. After that, a mordib silence fell on the theater, for obvious reasons.

On AOTC it was even funnier. People went crazy on the star wars logos again, I could hear some "oh no's" over the audience when Jar Jar appeared. People laughed when Palpatine said he "loved the republic" or something like that (regular audiences didn't even understand it), and they were all excited (there were some laughs) when Yoda fights Dooku. And I remember some people silently going "wow cool the death star" when the death star plans appeared (which is my favorite prequels moment). Hehehe there was this guy with a Bobba Fett helmet, I wonder if he took it of to see the movie. Can't wait to see what'll happen when episode 3 ends. I predict massive riots on the streets, followed by a violent bloodbath.

And... why does people applaud a movie? The actors are not there! There's nothing there! It's only light on a screen!