Some people, but not this person. I like having a separate login for each web service. I keep each login in my password wallet so even I don't know the password. Using this approach, if a service gets compromised, I don't need to worry that my access will spread to other systems.

I also like email/password signups because I get to use different emails for each service. GMail helps with this since I can use johndoe+twitter@gmail.com and johndoe+facebook@gmail.com.