bitcointalk.org is spending millions on their new forum system that's being written from scratch. Hopefully that will be one to look out for when it's complete.
It doesn't look like bitcointalk.org is using the calendar feature. :(
What's wrong with a google calendar? I'm pretty sure you can embed it.
Google calendar would require double entry. Right now the calendar links directly to forum posts and can be created, edited, and deleted at the same time. There is also an issue of moderator training if the site gets larger or someone else takes over after me.