Mamet is the shit. Few movies are as quotable as Glengarry Glen Ross. Hell, in Boiler Room characters sit around watching Glengarry and quote from it. Mamet has influenced an entire new generation of writers. I can detect traces of Mamet in PT Anderson and QT's work.
As for Paddy Chayevsky, I will give him props for foreseeing the future of television when he wrote Network in the mid-70's. In many ways, the world he envisioned has come to pass. However, I think a lot of his dialogue is way too on the nose. There are lots of bombastic speeches in Network, some of them are great, others go on long after the point has been sledgehammered into the audience. Time Magazine hit the bullseye when it said Network was an anti-youth movie, as Diana represents the new generation of cutthroat executives (now known as yuppies), and William Holden represents the virtuous old guard. I agree with everything Chayevsky is saying about popular culture and corporate control of the media -- I just feel that the way he goes about making his points is way too ham-fisted (like much of Oliver Stone's output).
The opposite approach is employed by Terrence Malick, who creates characters who communicate more by what they don't say, or what they aren't able to articulate. Sometimes, one look can say as much as a page of dialogue.
