I heard that Diablo's agent actually found out about her and her blog while surfing for porn on the internet. She exploited her past as a stripper quite well to gain attention, though now there is some backlash against her. In this generation it makes sense that this would happen: porn, tats, mixing with mainstream movies. Everyone needs their break no matter how you get it!
I have not seen Juno, but some of the previews to me suggest that the dialogue for the 16 year old girl character is quite advanced and perhaps a bit beyond what a normal 16 year old would use in real life...but that is ok if it works for the film which it obviously did.
Probably the biggest elements in getting this done is persistance to continue writing every day, not getting to critical over your first drafts just keep refining, and then having the social ability and sack to go out and shop your material. The
http://www.wordplayer.com/columns/welcome.html website has a lot of articles and columns from the authors who have successful careers, on how to successfully pitch your material and get it in there.