I love qaf_marathonsand I suck for not finding time to play there recently. You can always comment on past discussions or join in on the new ones. AND the best part is that you can talk about something deep and meaningful or just say how pretty Brian and Justin look :)
Here is a discussion I particularly enjoyed episode 214.
A community that I don't think gets used near enough is qaf_bunnies. I wish there was a new plot bunny there every day :)
happier_bunny had to ask a few times for someone to write her Pretty Woman plot bunny before dirtylttlescret came to the rescue, but if you ask me it was worth the wait.