I posted this in the early days of Office 2013 appearance but somehow its disappeared so I'm posting it again.
Calendar peek is an almost pointless waste of time compared to the To-Do bar in Outlook 2003-2010. Colour coding tasks and having them display under the Calendar has helped me not lose sight of those "Never get Round To" tasks. But the out and out winner in Outlook 2003-2010 is drag and drop mail to appointments. When you open the appointment the contents of the mail is displayed. Drag the mail to the day and all you have to do is put in the time and your done.
Its not there in Outlook 2013! What's that about? Its like someone sat down from a competitor and said lets make Outlook unusable for everyone so that we can sell them our product! The only thing worse I've seen is the removal of "Insert picture from scanner or Camera" from word 2007. Seems like its been down hill since 2003. Who's running this show?