mrkprc,
I, too, am looking for a running club and am moving in a couple of weeks. I know that there is a frequent but low key hash run on tuesdays(
http://bitch.harrier.ch/ ) that my wife ran with on her last visit. According to her they are very laid back, but a great group to run with. There is another group
http://www.zh3.ch/ to look at as well.
As I said, I'm not there yet, but we are moving in 3 weeks. (We will also be on the west side of the lake.) My wife and I both are training for a marathon in the fall. I am not sure what you mean by serious. If you are talking distance, then I/we are keen to do serious distance on the weekends with shorter runs during the week. If you are talking shorter / fast paced runs, then surely there are others who would be more interested.
We are part of a pretty big running community at home, and are eager to continue our social aspect of the sport. I was hoping to generate some buzz for a running group on this forum after I arrived, but your post prompted me to respond earlier than planned.
So, while your original question still stands (Running Club in Zurich?) If we don't find one, is there anyone interested in getting together for a run?