Welcome to Zürich.

You might want to check out these threads:
Mountain Bike (MTB) Tours/Trails in Switzerland
[Zurich] Mountain Bike Meet Ups (2008)

Also keep an eye on the calendar, we tend to organise a spin up Uetliberg every Tuesday. Though we tend not to get it posted till Monday sometime. Most of the crew on these rides seem to be into the whole pedaling up the hill idea. Lunatics. But I try and get out and do some lift assisted runs as many weekends as I can.

A few of us will be out of town this weekend doing this http://www.bike-attack.ch/. So recovery from that could determine our participation in a ride next Tuesday.

But look forward to meeting up with you in the near future.