I just finished directing a melodrama for a middle school.  Generally our high school and middle school students are quite well-mannered--but after turning around three times and instructing a row of high schoolers to be quiet, I had to threaten them to be quiet or I would remove them from the auditorium.  (as a teacher and a director, I have that authority)

A few years ago, I took one of my classes to see Shakespeare's Pericles at a local rep company.  Our group was split, so I was sitting apart from a few of the students, but my other chaperons were right above them (and did nothing).  Right after the play, there was a discussion group that the actors were going to hold with the school students.  The actor who played Pericles actually started off by discussing theatre etiquette, because some of my students had decided to "take a nap," "chat," "lounge," etc. in the front row.  Nothing got their attention better.

As for the cell-phone issue, we've created a special "performance" any time a cell phone goes off in the audience.  We stop the play, play some march music, have a few designated actors run out on stage, ask for the phone, talk to the caller and tell him he's interrupting a play, and put a cheap, ugly, decorated hat on the offender's head.  Then we hand back the phone, with the phone turned off.  (This is, of course, after we have written the standard note in the program, made at least one annoucement before the show begins, etc.) 

Are audiences rude?  Yes!  What can we do?  Educate them!  Will they listen/learn?  Probably not. 

I just finished up the show Nunsense, I played Sister Mary Leo and the audience last night was one of the rudest that I have ever had.  This one person was eating chips of some sort (a no-no of course) and they kept crinkling the bag.  And of course the cell phones with the really annoying rings not the good old fashioned "ring ring" but the latin music and the rap songs.  Also, this one woman kept singing along, which is fine, but she was louder than we were!