I love being able to log in using an OpenID provider rather than creating an account.

Because it's one less !$@%!@$! password to remember. Or it's one less $@&%!@$ hassle adapting my password creation formula to a new site's password requirements. Or it's one less place where my don't-care-use-it-everywhere username/password key is stored, perhaps @$2(! in the clear. Or perhaps it's just one less time I have to type in a @$@(%^! username and password. Or @*($&%! create one.