"I was only in one of the John Hughes films, and I never saw the other ones. I didn't understand them. I kept hearing a really hip 40-year-old person talking in teenagers' mouths."-John Cusack [NYTimes]
Personally, I think it's nearly impossible to get teen dialog "right" because it shifts and changes and is not only region specific, but also tends to be specific to groups of friends. Everyone I knew then and now developed a short hand of quotes and experience related isms that no one outside that would likely get.
Which is actually what I think Hughes got right. Not the precise way of speaking, but the way teens relate to one another and develop their own dialects. And often attempt to speak "up" or older.
Granted, there are some huge problems in his movies. Sixteen Candles is really, you know, racist...and Breakfast Club has that really misguided makeover. But Some Kind of Wonderful actually does attempt to get at some class issues. They're teen comedies so I don't expect deep discourse. But I think they did have heart and were attempting to capture something that's pretty elusive and transient about adolescence, but tends to influence in ways both major and minor the rest of out lives.