In Dallas, we've used Meetup.com to organize meetings. Meetup has a lot of great tools for getting together and organizing your group -- and it's FREE. Someone just has to take the lead and become an organizer. It's very easy and doesn't take very much time.
There has been talk about getting a National Prius Event. I think that is probably only going to happen if people start meeting locally, first.
There are already Prius Meetup Groups in San Diego, Manhattan Beach, Santa Monica, and Pasadena. You can find these groups at http://prius.meetup.com/ They probably just need someone to take charge and organize! This could be you!
There was a meetup with the LA/OC group on PriusChat a few weeks ago. I tried signing up on Meetup.com in the past, but nothing seems to be happening there. There was talk at the PriusChat gathering of meeting up again in a month or two.