It would be interesting a way to list (and manage, if possible) the pairs Users/Projects in the Role management page (not in the Roles list).
It is also useful to delete a Role, because if at least one User is of that Role for some Project, it isn't possible to delete and is necessary to find which are the Users that use that Role.

I think that redesing the Role management page in a way similar to Group management page, it could be a clean solution. So with three tabs: "General", "Permissions", "Users".