How does the User Card popup work?
I've noticed some users have a nice hovercard effect on the avatars that appear on their answers/questions.
What's up with that and how can one get such a nice hovercard?
From my observations, it seems users with over 2000 rep get them, but I'm not sure. It's just that everyone with high rep seems to have one, while users with 1k or less never.
I've looked on the stackoverflow privileges page and found nothing on that and neither did a search on "hovercard" or "profile" here, on meta, revealed anything useful.
Also, is this a network-wide feature?