I'm modeling the idea off of Muse Fusion, which is a creative jam thing we're doing with Torn World. We designate a day, where anyone can stop by and give us prompts. (In the case of Torn World, the prompts had to be for Torn World.)
You can see the actual Muse Fusion here: http://community.livejournal.com/torn_world/13878.html
and the wrap-up here: http://community.livejournal.com/torn_world/14454.html
As you can see, it was pretty fun - we ended up with a lot of material at the end of the day, and everyone had a good time.
For the Sketch Fest, we can do anything in the fantasy/sci fi genre, or particularly portraits, maybe, for PA? So, Joe Public can stop by and say 'green-haired rock goblin!' and one or more of us sketches a green-haired rock goblin. What we do with that sketch? Entirely up to you. I recommend putting it up at PA (with or without customization options) and sending a link to the person who left the prompt, sort of like a really, really fast submitted description. Or maybe it becomes the sketch for your next big piece. Or maybe you hide it from the general public forever. You do not need to submit any of your work to PA or EMG, you can consider it just a fun art exercise or... whatever you want! The idea is that we have a fun time and make some art. If some of it ends up saleable or gets adopted, so much the better!
I recommend not spending too much time on any one piece - think of it as a speed-art day. I also recommend letting folks know if you're working on their prompts - partly so that we can spread out our efforts and make sure that everyone gets at least one prompt responded to (depending on how many people participate!), and partly to encourage audience participation. Artist participants can also put out paypal tip jars.
If this sounds like fun, let me know, and let me know what day might be good for it. A weekday is better for me, maybe 2 weeks from now?
Comment here, or at the forums and we'll work something out...