Unfortunately, Facebook kind of runs my scheduling life. I plan events there, accept events from other folks for parties and recitals and stuff, and–most importantly–keep track of many birthdays that I’ve never really put into my calendar over the years.
The last couple of OS X iterations have required some bit of effort to make the Facebook calendars show up in the Calendar app, though. Mavericks changes that by making it chimp simple to get your Facebook events connected to your Calendar app.