The privileges page about established users in Ask Ubuntu reads like this:
An expanded usercard is only available if you have have at least 28 characters in their "About Me" section of their profile.
However, I found a quirky bug today when I noted an usercard of an user expand even when he had 0 characters in his "About me" section.
It even has a drop shadow effect on the avatar as if the usercard was supposed to expand on mouseover.
I used this question for checking the bug: