When I add the create user capability to (for instance) the subscriber role, they're able to create users that have the Administrator role (well, I've found that they also need the edit users capability, but that's not the point).
I think it's a bit funny that users can create other users with higher roles then their own. Is it possible to give them the ability to only create users with max. their own role? (if the create/edit users capabilities are enabled for that role, ofcourse).