OK I intend to start developing the calendar. With the forum upgrade I have added a new feature.
http://www.zclub.net/forum/calendar.php
When you add an event be sure to check the field that says "Allow users to specify they will be attending this event".
This then allows people to click "I will be attending this event" and also un-attend the event, and allows you and everyone to keep track of who's going easily. I would recommend that if you add an event in your forum you put a link to the calendar event in your first post. I will work on adding attendance directly into the threads another day.
I will work on making the calendar more friendly and visible over the next few weeks.