What I've always been told (YMMV) is that if you can't sell your pitch in two sentences, you're pretty well fucked. You've got to have the ideal of what it is in your head, and sell them on that; not what it will be but what the core of the ideal is.
if i ever have another concept, i'll only post the logline next time.
this is fleshed out, as well as parsed down to cover letters, synopses, etc to the appropriate persons.
Don't even post that much. Do it not get it: You post NOTHING till you have a contract or a firm denial. NOTHING. That's the professional way of doing it.
If you haven't, invest in three books: Screenwriter's Bible, Screenplay: The Foundations of Screenwriting, The Complete Book of Scriptwriting Read 'em cover to cover and pay attention to the sections regarding the business side of things.