I can't speak for him, but I never use Facebook auth to prevent scumbags from getting a bunch of info about me including a list of my friends with no questions asked.
a) it takes a longer relationship where I'm treated with respect before I trust a site. I'd have to know they weren't going to spam me or my friends, they weren't going to store tons of data, things like that.
b) most of the info I put on FB is fake, I only keep it to untag photos. FB doesn't fit criteria a, haha
c) pretty much everyone trying to get at my social graph
And contrariwise, I never use Facebook auth to prevent Facebook from getting even the slightest amount of information about my usage of other sites that I can avoid giving them.
