This may be a limitation of using the Flag module.... but is there a way to make overlapping "Add to My Schedule" flags mutually exclusive during a given time slot?
If one puts limits on room occupancy, then it would be possible to "block" other users from signing up for a slot/position in a session by adding more than one session item to their agenda.
The attached shows three different sessions with the same time slot added to the users "My Schedule."
While starting this process... I also found this. So I might be answering my own question.
http://drupal.org/node/563520#comment-2197222
This might be a better fit in the COD Support Issues queue or Flag module, but I wanted to ask first before putting it in the queue.... sorry, too, if this has been addressed. I'll re-review the forums, issues queue, etc.. for answers.