Django: When extending User, better to use OneToOneField(User) or ForeignKey(User, unique=True)?

I'm finding conflicting information on whether to use OneToOneField(User) or ForeignKey(User, unique=True) when creating a UserProfile model by extending the Django User model.

Is it better to use this?:

class UserProfile(models.Model):
    user = models.ForeignKey(User, unique=True)

or this?:

class UserProfile(models.Model):
    user = models.OneToOneField(User)

The Django Doc specifies OneToOneField, while the Django Book example uses ForeignKey.

James Bennett also has two Blog posts that providing conflicting examples as well:

• Extending the User Model
• User Registration

In the former post, Bennett provides some reasons why he switched to using ForeignKey instead of OneToOneField, but I don't quite get it, especially when I see other posts that recommend the opposite.

I'm curious to know your preference and why. Or, does it even matter?