ps...i understand about not want to post the links to the fics in advance so people don't run off and read and then forget to comment. but maybe you could post the link a day or two in advance, especially for longer fics. just a thought. i think it's totally fine waiting too, but it would be nice to read a bit in advance so you can jump right into the conversation :D
you could post a link as a pimpage/reminder of the dicussion to follow in a day or two and put a no comments lock on the reminder post so people don't start talking about the fic in the pimpage post :D