I have been using ipb for a long time and they do have a nice apporval tool on their calendar system...
User can submit a new event and if you set the calander as you as admin approve all events and dates, the post stays invisible to the public untill you approve it...
If you want to delete the event, just click a button on the form and that's it...
Here is the screen shots...
First one shows that there is a invisible event submitted by users....
Second one shows that if you click that invisible little icon brings the event.
You can aprove (make it visible)
You can delete
You can edit...
All on the upper right side corner....
This is a good function... and easy submit and approve feature...

