I think birthdays helps Facebook improve engagement with its users, and allows for Facebook to achieve their goal of connecting people. For instance, I often use birthdays as a way to re-spark conversations with people I haven’t talked to in a while. Some metrics that could help summarize performance include:
1. % of users posting on walls for birthdays on a given day (assuming birthdays are evenly distributed across the days of the year)
2. % of users messaging friends for birthdays on a given day (assuming birthdays are evenly distributed across the days of the year)
3. % of users using Google calendar link to Facebook birthdays
4. % of users clicking on birthdays section of Facebook through the notifications list versus bookmark
5. % of users in the birthdays section then actioning on birthdays section of Facebook
6. % of birthday wishes that lead to a conversation