Seriously? I just added the people important enough to congratulate outside of facebook to google calendar with a yearly returning reminder (oh, and birth year, not unimportant)
Just before quitting Facebook, I made a point of adding friends' birthdays to my iOS contacts, which are shown in the calendar on my iPhone. However there is no option to be automatically reminded of all birthdays, so I still sometimes miss them. I feel like this should be available as a standard feature of iOS.
I'd pay for an app that would simply read all the birthdays from my contacts and create a calendar reminder for each one. Not a monthly subscription, but definitely worth paying a few pounds for.
Not sure about iOS, but on Mac OS X calendar: Preferences > General > Show Birthdays Calendar.