The rudeness of theater patrons really depends on where you live, what specific theater you go to, what movie you see and also what time. If you live in the suburbs and hit the multiplex at 9 PM to see the latest summer blockbuster of course it will be overrun with rude, blabbering, cell-phone using, obnoxious teens. More mainstream films in more mainstream theater locations during peak hours (ie 7-10 PM on weekends) produce the biggest percentage of obnoxious patrons because during this time a lot of people there aren't there just to see the movie but to be part of a social engagement, so you often have larger groups of people that are at the theater after dinner but before they hit the club or whatever so their attention is more on the social aspect of being there rather than actually enjoying the film, hence you get stuff like cellphone ringing, saying stuff at the screen, and group chatter when more than four minutes goes by without an explosion or car chase.

I personally don't see a lot of the blockbuster type films anymore so I don't really have to deal with this stuff. I've found that most audiences even in such a hugely populated area such as downtown Toronto are pretty decent even at the city's biggest theaters; its more about the type of film itself--I'm sure the experience of watching Fast and Furious 3 in a theater would be more painful than the actual film because it attracts a lot of people more prone to be jackasses. There's also the fact that rudeness varies on a regional basis--usually in areas less metropolitan in my experience, but again, my theory is that its entirely dependent on the type of film myself; if you were to see a foreign film in a Florida suburb (just hypothetically) chances are that the one or two people in the theater would be there to enjoy the film and would be respectful of the enjoyment of anyone else in the theater, whereas if you were to see Spiderman 3 in the same theater chances are it would be packed with a lot of people that would make for an irritating viewing experience.
I'm not sure why, but just based on reports and observation, this whole thing as a significant problem seems to be more prevalent around the southern US states; movies have always had annoying patrons, and certainly it seems to have sharply increased since the late 90's, but I always hear of the worst problems from the south US for some reason; maybe films just aren't treated as seriously there? I've noticed that rude patronage sometimes corresponds to a lack of respect for whats onscreen.