I work as Surround Staff for a summer Writer's Retreat called "Squaw Valley Community of Writers." I'm in the screenwriting program, although there's also a novel program. For the last 5 years I've been with them, spending a week in Lake Tahoe working on a script exclusively with other screenwriters.
You work with a mentor, who reads through your script in advance and then, each afternoon, has a small group of students that they meet with in groups and one-on-one. They know your script in advance so you get a lot of direct attention on your specific story, which was a huge help for me early on.
I do surround staff, which is basically like setting up the DVD projector and the like. I attended on a scholarship my first year and have been going back since just to help however I can. Hashing out problems in my screenplay with a seasoned professional was great for understanding screenwriting as a whole, and spending a week lodging in this mountainous resort was inspirational for the new ideas I'm always looking for.
Here's the official copy:
The Squaw Valley Screenwriting Program focuses on individual attention and work-in-progress, mentored by award-winning writers and writer-directors. Crystallize the story you want to tell, and excise extraneous elements. Designed for both screenwriters and filmmakers, this unique program invites both narrative features and character-driven documentaries that are currently in development. Our goal is to assist writers to improve their craft and thus move them closer to production.
Deadline for application is May 1, notification by June 10. Check our web site for further details: www.squawvalleywriters.org/swriter_ws.htm
So I can answer any questions, but if you're interested in taking a week to really work on your idea, this is a great way to do it.
EDIT: Just in case there's any issue, I'm not involved with any of the acceptance process or sales or anything like that, I just handle some staff stuff during that week and post around about it.