Spotify was doing it when I tried to join. They apparently changed it later, to not require Facebook. But, you know, first impressions being what they are, I'll never be a subscriber. Trust is hard to recover once lost. Guess Google is going to find that out the hard way.
Oh, it works without FB again? I joined when it was new but never used it much (niche musical taste). When I tried to login again a few (4-12) months ago, it wanted to force me to use FB so I just started ignoring them altogether.
And as a result, I never used Quora.