Facebook just added another extremely useful feature for users, and in doing so took out a slew of applications that do that same thing. You can now get a weekly email telling you, simply, which friends have birthdays coming up.

That’s good news for all of us who want more birthday information. It’s bad news for Birthday Alert and its clones that already do that on Facebook. Birthday Alert has 180,820 active monthly users.

Lest you think this is just some random feature: Birthdays are big business. Bebo founders Michael and Xochi Birch started their social network Bebo with a simple birthday reminder service. That service had 100 million users at one point and still brings in $4 million per year in revenue from ecards and gift purchases. Bebo was funded in the early days from birthday reminder revenue.

The title of this post is meant to be a joke, but it definitely sucks to be one of the very many birthday reminder Facebook apps today. Such is life. With a flick of the keyboard Facebook can make your app redundant and pointless. Meanwhile, I happily turned on the new feature, and I can’t wait to be prompted to send people virtual birthday gifts for a small fee.