> Erm, Facebook did implement something like this. Shortly after Google+ came out. You can still assign friends to different groups.
IIRC, Facebook never really promoted those features or tried to make them easy and intuitive to use. Recently they've also made changes to make them less useful.
It's sort of like difference between having a well-designed and usable feature or a similar feature that only exists to check off a checkbox.
They were easy and intuitive. Facebook didn't promote them for the same reason the circles in Google+ lacked traction: The majority of users didn't care and didn't want it.
IIRC, Facebook never really promoted those features or tried to make them easy and intuitive to use. Recently they've also made changes to make them less useful.
It's sort of like difference between having a well-designed and usable feature or a similar feature that only exists to check off a checkbox.