One of the cool features in Outlook 2007 with Exchange 2007 is the ability to specify the expiry date for sending automated responses (Out of Office).
All of us who use Outlook have definitely benefited the "Out of Office" Assistant which sends an automated response to the sender for once (and different options) with a customized message stating your absence and the ability to provide your emergency contact details, alternative contact person etc.,
With Outlook 2007 and Exchange 2007 you can specify an auto expiration for the "Out of Office" replies. Many of us would want to avoid "Out of Office" replies to go even after our vacation and particularly, if we forget to remove that option.
Go to Tools - Out of Office Assistant - You will find the Send Out of Office replies only during this period, where you can specify the period till you want the replies to be sent.
Secondly, you can find the option for sending a different response to senders within your organization as well as people outside your organization.
This would benefit you largely since you may want to send some specific information for senders within your organization and a different message to others.
I am sure this is not one of the best features but definitely one which I liked very much.
Cheers.