Currently, when trying to add someone to a course using the people picker that is already enrolled, they simply do not show up in the pick list.  This confuses many of our Admins, who don't already know the user has been enrolled.  Ideally there would be a notification that the person you are searching for is already enrolled.

Likewise, it would be helpful if there were a similar notification when trying to pick a course to enroll a user into from their profile page that they are already enrolled in.  Today the course simply does not appear, which looks like an error.  Ideally a notification would appear indicating the user is already enrolled into the course you're searching for.