I noticed that some users have a "pop out" profile, and others do not. It doesn't seem to be related to reputation, nor if the profile was indeed filled out.
What permits some to have this feature and not others?
Have a look at this question on MSO .
It suggests a minimum of 1k rep, and a minimum amount of text in the about me field
answered Oct 11 '11 at 16:43
It is thoroughly documented on the "established user" privilege page: you get the "extended usercard" when you both have at least 1000 reputation, and the "about me" section of your profile contains at least 28 characters. There is a syntax which you can use to override the text in the popup (or even disable it).
When there is an expanded usercard, the user picture is displayed with a drop shadow.
