Michigan has many organized rides through the Cycle Conservation Club of Michigan (organization started back in 1968). This organization is responsible for all of Michigan's great trails throughout the state.
Here is the listing of all 2008 events:
http://www.cycleconservationclub.org...cc_events.html
Of course, there are also tons of hare scrambles and enduros throughout the year. In my opinion, the CCC events have great turnout and a better atmosphere for Demo rides.
Here are some of the most popular CCC events:
The first event of the year is called "Rites of Spring" (May 3 & 4) and attracts up to 800 riders. I have not ridden yet in the CCC events, but others that I have spoken with say the turn out is great and a lot of fun. Here is more info on the Rites of Spring. The Atlanta trail system where this event is held has some great terrain.
http://www.cycleconservationclub.org...ds/ROSTT07.pdf
The most famous event is the Six Days of Michigan (July 20-26). The event is held in the Grayling, MI area. One day, I definitely want to do this one... perhaps this year!
Another great place to ride in the Mio-Hunt Creek trail system. There is an event on Aug. 9 & 10 for this area. This place has great singletrack and a variety of soil conditions.
In the fall, a popular event is the "Fall Color Tour" held in Rose City (Oct. 4 & 5). There are typically lots of people at this event, similar to the Rites of Spring.
If you are interested in setting up a Demo ride, I would suggest you contact the Club president and/or trail coordinators. Here is the contact information:
http://www.cycleconservationclub.org..._contacts.html