I quit and deleted the account, however, when the demands of reciprocity got not only too time consuming, but too transparent and formulaic to participate in without feeling almost ridiculous.
It is tangentially related to a scene from Fight Club-
Narrator: When people think you're dying, they really, really listen to you, instead of just...
Marla Singer: - instead of just waiting for their turn to speak.
On Facebook, as with many social media sites (including Flickr), people "listen to you" to remind you that you should listen to them. They like your posts and comment on your pictures and send you happy birthdays all to ensure that you feel the obligation to do the same to them.
Life is full of that sort of reciprocity, but never could it be piled onto people with the easy lack of friction that Facebook affords.