Do you use a calendar on your forum? When Christianity Haven was started, we had a calendar and it was nice to give me reminders of things. Members never used it and I think I was the only one, so what was the point of keeping it.
I can't say I have ever found a use for a calendar myself. Something such as a way to have to-do's on my forum would be ideal but a calendar I feel would go without being used.
I keep meaning to add a calender to my server, but under a subdomain, in order to plan when to write or post thing. In terms of the forum though? I'm not sure it would add much value, while adding a little more unnecessary complexity.