"...there have been multiple other apps that required me to use my Facebook credentials to log in. Facebook, it seems, is now core to the mobile Web experience."

Most social networks provide very little that a blog and an email address don't, and for that modicum we pay with our privacy. Personally, I don't think the convenience of OAuth is worth what the networks earn from selling my data. I wonder what'll happen to their market share when smartphone OS developers start including authentication layers in their kernels.