I think it would be massively beneficial to be able to put your re-call calendar on "Holiday/Out of Office".
I understand most in the office know of your absence when your away, but they don't memories your holiday dates for the future.
It would stop you coming back to potential many missed opportunity's and a potential back log which other could be dealing with whilst your away.
A system option to either:
Allow the setting of a task but warn the users who set the task that you're out of office date X until Y
Completely stop the setting of tasks over you out of office period
I can see user cases for both of these scenarios.
This would be a very useful feature for a sales team all being on one page - it would mean that they can schedule calls in confidence that it will be completed. Especially if a task is being scheduled for another team member.