We currently have the option to 'not receive out of office' notices in the delivery options of an email. It doesn't work very well, but the concept is good.
I would also like to have an option of 'Do not deliver to recipients who are currently out of office'. I frequently have to send out 'all staff' type emails that contain information that is immediately valid or only valid for a short space of time. I always feel its a little unfair that recipients who are out of the office should receive these when they are not relevant to them.
You would also need options as a recipient to over-ride this if you so choose.