Why I'll never pick the 'sign in with a Facebook or Google account' option
Recently I read Mike Hearn's Building account systems (via), where he strongly recommends that people not build an account system themselves but instead outsource it to Facebook and Google via OAuth. When I read that, I winced; not just at the idea of having 'sign in with ...' as my only option, but also because Mike Hearn's arguments here are actually solid ones. As he covers, it is a lot of hard work to build a good web account system and you will probably never be able to do it as well as Google and Facebook can.
I have any number of moderate problems with big-site OAuth, like how it gives Google and Facebook more information on my activities than I like (information they don't normally get). But this is not the core reason why I assiduously avoid 'sign in with ...' options. The core reason is that when I sign in with OAuth, my Facebook or Google account becomes a central point of losing access to many things. If Google or Facebook decide that they don't like me any more and suspend my account (or lock me out of it), I've probably lost access to everything authenticated through OAuth using that account. If I had to use 'sign in with ...', that could be any number of things that I care very much about (for example), far more than I care about my Google or Facebook account.
Facebook is far more dangerous here. Google generally doesn't seem to care if you have multiple accounts, while Facebook wants you to have only one and may suspend it if they decide that you're using a fake name. It's nominally possible to make a separate Google account for each site that demands you sign in with Google; it's not with Facebook as far as I know, at least within their Terms of Service.
(The other issue, as seen in an interaction with LinkedIn, is that using these sites as OAuth sources requires agreeing to their TOS as well as the TOS for the site you really care about. But then, everyone ignores TOSes anyway because if we didn't we'd all go mad.)
I have never personally been locked out of my Google or Facebook account (although I did worry about G+ stuff before the Google Reader shutdown). However, on a global scale it happens to plenty of people (anguished stories about it show up periodically in the usual circles), and I actually know someone who is currently locked out of their GMail account and is rather unhappy about it. As a result, I very much want to separate out all of my online accounts and I basically insist on it. So for entirely selfish reasons I certainly hope that web sites don't listen to Mike Hearn here.