What a brilliant concept! A place where you can find group rides, routes, who's riding and when. In 90% of the USA this website is worthless because there is just that 1 ride going off in your area but in the Front Range there are more group rides heading out than there are riders in those "other places" in the USA. So how do you find a group to join? Just ride slowly out on a road until one passes you and you jump on. That method might work or you could waste a training ride being a wall flower on the road.
I like this concept so much that over a year ago (before I discovered this website) I was writing my own web application to do this very same thing. The app is pretty empty for our area so to make this work we need to start using it. Give it a test ride and tell us what you think. It's not quite like I was building mine but close enough.