Everything that I've come to understand about the process of screenwriting, from the initial idea, right through to a finished project has been learned on Trigger Street Labs. I've read a few books on the subject along the way, but nothing as valuable as learning to give constructive, and structured feedback and notes on projects.
Reading screenplays, whether amateur, or professional is a great way to learn about your own writing.
It's a great loss to the screenwriting community.
But not all is lost.
There are three or four avenues out there where you can go. Probably a few more. But these will keep you occupied.
Done Deal Pro Forum
You can discuss all things screenwriting here. Free forum, paid membership.
Much like Trigger Street Labs, you can upload work for feedback and notes, once you've given notes on projects, and collected enough dollars. It's also a place where you can showcase your work. Free, and paid memberships. A link to join up is below.
The Black List
While a great resource for screenwriters, I would advise against using it until you've work-shopped your script, and gotten feedback and notes on it, and made it the best it can be. Uploading a first draft to the Black List isn't going to do you any favors. You want to give yourself the best opportunity, and not squander it. Unless of course, money is no object.
Russell's Screenwriting Forum
I've created a small forum here. It's nothing fancy, but it's easily accessible and easy to use, I think. If it doesn't get any bites or interest, by the end of January, I'll remove it. Feel free to use it for feedback and notes. And anything writing related.