It would be nice to have the option to out an out of the office connected to your Full day appointments in your calendar : as an example, you could have planned going to TechEd, and you already know who would be your backup, so you could already set your OOF at that time linked to that appointment, so that the OOF is automatically send during the time of the appointment (in the example while you are at TechEd). same for Full day intervention or visit at a customer, you could set already your oof, so that when you receive a mail, the sender automatically gets notified that you won't be able to respond immediately. (could also be interesting for shorter appointments e.g. half day appointments).