Insprired by a posting by Agnus I thought about the Ipernity groups too.
The groups in their current implementation are quite boring and too chaotic in my opinion. Since there are just too many pictures (including a lot of mediocre ones) no one seems to care to browse a complete group.
I really would like to see some kind of rating system with the option to show the best pictures of a group first, instead of the latest posts. Additionally this little rating competition could be used to adjust the maximum number of pictures a person can add to a group simultaneously. So users which added highly rated pictures might be allowed to add some more, while others would have to remove some of their older posts first, to limit the total number of pictures in a group somehow.
Another annoying thing are the huge amount of duplicate groups with exactly the same content (for example cats). Maybe an official group tree managed by Ipernity (like animals.cats or people.portrait.woman) would be a nice addition.
A feature I would propose is an invitation system for pictures. So when a group admin sees a picture he wants to add to one of his groups, there should be some "Invite this picture to group X" button. The creator of the shot could be asked during his next login, if he wants to allow or deny the request. This would be much easier then the current "read request comment, join group, post image" system.