Regarding the lesson about being a friend vs. being a pal, I agree that being too chummy can be dangerous and blurs the professionalism line, not to mention the impartiality one needs in a classroom environment. But I believe developing closer friendships with ex-students is acceptable. Once you no longer have sway over their grades or them meeting the requirements of your course, there's really nothing to prevent deeper friendships from forming, especially if said friendships lead to professional projects together.
