One of my favorite features in Mountain Lion is Notification Center. I have been using Growl for years, and the impact Notification Center has on my workflow is very similar, and it’s an added bonus to see it on both my iPhone and now my Mac.
In Calendar, you can set alerts for birthdays and events, as well as turn off any shared calendar notifications and invitation notifications. Why is this helpful? I like to see a window pop up reminding me that it’s [insert someone very special here]‘s birthday, so that in my increasingly hectic life, I can make sure I won’t forget. However, I don’t need to see every single event I have going on.
To get there, go to Calendar (formerly iCal) > Preferences… > Alerts. Then, customize as necessary. Of course, this works best if you actually have birthdays entered for your contacts, so if you do that, and then actually pick up the phone once you’ve been notified, your friends and family will thank you!