hi Jessy, I created a p2pu group some time ago, but no one joined so far, except for Philipp and Rebecca Khan. I use Mendeley extensively, and think it is one of the best reference managers (but which can still improve a lot). Anyway, the group is open to join, this is the link: http://www.mendeley.com/groups/2108343/p2pu-peer-based-online-learning/
EDIT: I just saw that you created a group on Mendeley as well. I have some signup problems, but will delete my group and join yours.