A place where I work recently upgraded Exchange. I interact with the calendar part of it minimally -- receiving appointment requests by e-mail in Mutt, and following a link in those e-mails to a web interface for accepting or declining.
One of the 'enhancements' is that the web interface now takes it upon itself to alert me to imminent appointments. And indeed to ones that I've missed. Where it interprets 'missed' as me not having bothered to acknowledge its reminder. The particularly fun part is that during the years of its web interface (or at least the one served to Firefox) not having 'acknowledge this appointment' functionality, it'd still been quietly building up a list of all my appointments and noticing that I hadn't acknowledged them. So the first think I see on logging into the new system is a message nagging me that I'm 1773 days late for an appointment. With my last- boss-but-one, who left the company several years ago. In a building which no longer exists. Thanks, Exchange -- that's just what I wanted to know! Smylers