Critique Groups: Open/Closed

Got an email the other day from a writer who's aiming to set up something similar to the GSFWC in their own town and wanted to pick my brains. He'd noticed it was an open workshop, run along Milford lines, but some of the people he's got interested in setting up a critique group are, it seems, a bit worried at the prospect of being swamped in dross--shoddy copyism and outright fanfic. So, he