I really wonder if this falls under the category of "things hacker dislike/complain about but regular people don't care/mind"
I think Pinterest does this too. I'd guess most users think its a byproduct of Facebook connect and don't care. If I had a mass-market/consumer site, I'd consider doing it.
Heck, I'm a hacker and even I like the feature. Why else would I even connect my Facebook account in the first place, if not to use my established social circle there? You can join without Twitter or Facebook.
I think Pinterest does this too. I'd guess most users think its a byproduct of Facebook connect and don't care. If I had a mass-market/consumer site, I'd consider doing it.