making feedback public

I do a lot of comparing between teaching in online vs. live classes. I'm fascinated with the opportunities that online technologies provide that don't exist in live classes. This morning as I was typing individual feedback in the discussion forum to my students' most recent assignment, I was reminded of both the positive and negative attributes of making feedback public.

• Positive: I am modeling how to provide feedback in a constructive, growth-oriented approach (or so I like to think). Since most of my students are teachers, many desiring to be online teachers, this is a necessary skill for them to observe and develop. I always frame the feedback in terms of strengths and areas for improvement.
• Positive: Making feedback public encourages the development of community--that we are all in this, learning together, learning at our own pace and based on our own needs. I never assign a grade in public feedback. I think this approach helps to transform an outdated behavioristic approach to learning where the student has to "get it right," and the teacher's job is to grade the "correctness" of each assignment.
• Positive: Students can learn from other's work and my perceptions about that work. Many of my students report enjoying reading my feedback to others in class. It gives them an idea of how their work compares to others (performance anxiety?). It also reinforces the classroom culture I want to promote--that you are not competing with others in the class, but rather, engaged in your own learning process and professional development.
• Negative: Ok, so just how to tell a student, when needed, that their work really stinks? I mean, how "nice" can an instructor be when what you really feel like saying is, "Why are you wasting my time with this weak attempt?" This doesn't happen often at the graduate level, as I have a great group of students with whom I'm priviledged to work. But there are times when I will ask a student to reconsider, reread, and resubmit their work. Is this a form of public humiliation? Is it a turn-off to student learning? Can it be a wake-up call for that particular student? What impact does this type of feedback have on other students in the class? One approach I've used in the past is to publically type, "See my email for feedback" and then email that student privately.

I'm curious to hear how other online teachers have worked with public vs. private feedback, particularly on poor work. Any thoughts?