When are you going to be here? Here is a schedule for rides and events in the area for April -
http://hbl.org/?q=event/2009/04/02/month
The only group ride I've ever done is Tantalus on Wed afternoons. That is an awesome ride and the people were always pretty cool. The Haleiwa metric centry is on 26APR and that is supposed to be a nice ride, I'm signing up for that one.