I joined because I've been enjoying a lot of the stories here, and wish I had a little more writing talent to put some of my own ideas down on paper (or LCD, at least..)
It bothers my conscience not to thank the authors of good (free!) fiction for the works they've made available, and tell them what I liked or didn't.
What'll keep me coming back? Fun discussions. Being able to laugh about how our son raised his hand and said that we had plenty of rope at home at a scout meeting when they asked for stuff for some training class or other. (yeah, there were some giggles, and I think we might have turned just a liiiiiiiiiiittle red!)