I did find that an odd comment. I understand the assumption is that you will eventually roll your own (perhaps?) but to imagine requiring a user to be part of those services to use your own service, especially of your service has nothing to do with those, is very strange. Just a few examples of how that could become a pain for our pretend user Greg:
a) The obvious, Greg simply does not want a Google/Facebook/etc account.
b) Greg is from a region that does not have strong Google/Facebook/etc uptake and does not have one.
c) Greg is from a region that actually disallows those services, making your service blocked entirely.
d) Greg does not want to link his 3rd party account to your service.
Lastly if you are targeting enterprise clients:
Greg is signing up to your service for a company he works for, not for himself, and there is of course no "Company Facebook Account". If his company uses Google Mail then he is in luck, but if not then there is a whole new account management process to go through. Someone will inevitably leave the company, lose the credentials, forget they ever had an account in the first place or remember they had an account but forget the new 3rd party services password instead.
Not to mention, if you are running a company, relying on a third party for such an important part of the puzzle is putting an enormous amount of trust into that third party. I know there are lots of those trust connections to take into account in any business, but if I am in the business of writing software it seems odd for me to not have the confidence and ability to manage an in house accounts system.
a) The obvious, Greg simply does not want a Google/Facebook/etc account.
b) Greg is from a region that does not have strong Google/Facebook/etc uptake and does not have one.
c) Greg is from a region that actually disallows those services, making your service blocked entirely.
d) Greg does not want to link his 3rd party account to your service.
Lastly if you are targeting enterprise clients: Greg is signing up to your service for a company he works for, not for himself, and there is of course no "Company Facebook Account". If his company uses Google Mail then he is in luck, but if not then there is a whole new account management process to go through. Someone will inevitably leave the company, lose the credentials, forget they ever had an account in the first place or remember they had an account but forget the new 3rd party services password instead.
Not to mention, if you are running a company, relying on a third party for such an important part of the puzzle is putting an enormous amount of trust into that third party. I know there are lots of those trust connections to take into account in any business, but if I am in the business of writing software it seems odd for me to not have the confidence and ability to manage an in house accounts system.