Courtesy of Tanya Huff; file this one under tough love. The whole thing is worth reading; the excerpts are just what caught my attention the most.
The tone of the piece is, admittedly, on the snide side — but after having my own time wasted by wannabes, I empathize completely with the position he takes.
[Here is] an ugly truth about many aspiring screenwriters: They think that screenwriting doesn't actually require the ability to write, just the ability to come up with a cool story that would make a cool movie. Screenwriting is widely regarded as the easiest way to break into the movie business, because it doesn't require any kind of training, skill or equipment. Everybody can write, right? And because they believe that, they don't regard working screenwriters with any kind of real respect. They will hand you a piece of inept writing without a second thought, because you do not have to be a writer to be a screenwriter.
... It rarely takes more than a page to recognize that you're in the presence of someone who can write, but it only takes a sentence to know you're dealing with someone who can't.
(By the way, here's a simple way to find out if you're a writer. If you disagree with that statement, you're not a writer. Because, you see, writers are also readers.)
As you can guess, this applies to far more than just screenwriting. As someone in the comments said, "the more hopeless the would-be-writer is, the worst they take the news." (The comments, by the way, are divided between people applauding Josh for speaking truth to idiots, and the idiots who think Josh wrote this article because he's a blowhard who wants to show off the size of his reading pile. Or the idiots who think Josh is a hack because he gasp ADAPTED SOMEONE ELSE'S WORK shudder.)