Facebook has debuted a slightly revamped groups feature with the aim of guiding members toward using groups as they were meant to, at least in their newer incarnation, as a way for friends to get together, talk about common interests and so on.
One of the first changes you'll notice is the new Time-line inspired cover photo that, by default, displays the profile photos of the most recently active members of the group.
Group admins can change the cover photo to anything they want, as long as it fits in the header, it's smaller than the regular Timeline cover photo.
The new design also places the links to group events, photos and docs more prominently inside the header image, along with the members link.
Another addition is a prompt at the top of the right bar which asks "What should people post in this group?" to provide a guideline for group members.