I'm generally more interested in what others have to say here than in putting my own stuff out there (though I've almost certainly been guilty of brainspam on occasion)... There are people who are forced to sit in an office with me every day, so I already have an ideal captive audience for when I just want to delight in the sound of my own voice.
The forums (and the people I've met here) continue to introduce me to new things and ideas, stuff I wouldn't have encountered just going about my everyday life. I feel that by interacting with a broad range of interesting people, I become a little more interesting myself. And unlike in real life, pretty much everyone here knows what Monkey Island is, and I've never been ridiculed for getting excited about Doctor Who. Nice.
Quality is the kind of mixture I think you'd get pretty much anywhere you have a large gathering of relatively anonymous people. Obviously I see some sort of value here or I wouldn't have stayed around for this long.