Writing is a solitary activity, so "writers' group" is something of an oxymoron, isn't it? as evidenced by Jason's putting a singular possessive, writer's, before the group noun.

What can writers do in a group? One, they can stroke each other's egos, which may or may not be helpful to writing, probably isn't. Two, they can comment on each other's work, which likely amounts to stroking egos, etc. etc. Three, they can "network," awful term for an awful concept, but at least it may help get work placed, even though most publishing of new writers comes through established mentors, not equally-desperate peers. Four, they can get drunk and/or sleep together, which may give them some material for eventual writing, though I suspect that after a few thousand years both those subjects are just about exhausted. I know I am.

Dude, I had to work. Then I went to a bodacious dinner party. I'll tell you all about it later.