Speaking as just one guy, "log in with $service" is a bigger pain than "Sign up and log in". Sometimes I don't have $service, or I have it but don't like using it, or I have it but I don't want whatever new random thing I'm trying out to have hooks into it. (Anyone else seen in their Twitter feed a bunch of app noise followed by an apology?)
I dropped GMail about a year and a half ago. If any services I was using required it to log in, I would have had to drop them, too. I think it's mostly because I know a lot of programmers, but I do know a large number of Facebook "conscientious objectors" (myself included) who can't log in to things that require Facebook.
It's really nice to have services like this self-contained (as long as it makes sense; Twitpic, for example, would be less useful if it had no hooks into Twitter). I can pick the service up and if I don't like it, put it back down. And if I drop some account elsewhere or just change accounts, nothing depends on me having it to log in.
I dropped GMail about a year and a half ago. If any services I was using required it to log in, I would have had to drop them, too. I think it's mostly because I know a lot of programmers, but I do know a large number of Facebook "conscientious objectors" (myself included) who can't log in to things that require Facebook.
It's really nice to have services like this self-contained (as long as it makes sense; Twitpic, for example, would be less useful if it had no hooks into Twitter). I can pick the service up and if I don't like it, put it back down. And if I drop some account elsewhere or just change accounts, nothing depends on me having it to log in.