Blizzard has mentioned that they've been working on one of these for a while, and it's nice to see the results. If you look closely you'll see things like when the Darkmoon Faire is coming, and when the Stranglethorn Fishing Extravagenza is happening. It doesn't show what PvP weekend it is, but I have to believe that's something they'll be working on.
Check out the screenshots below for the new UI. I'm sure you'll be happy!
Update 12:57 a.m.: There is a way to add user events in the calendar. It also appears there is a way to share the calender items among individuals. More information incoming.