In order to go on an official run, you needed to be a member and do their course(s)... which was a bit pricey given must of us just like to get out and hit the trails for free. One of the main complaints I heard from others was people would sign up for a membership and then find out courses were not being run frequently (or cancelled last minute) so they couldn't go on the official runs sometimes for months on end.
That said, while I never joined their club officially, I did unofficial runs with them from time to time. I think the majority of the people signed up on their site did this, just too much hassle otherwise.