My Commander did something similar to an anonymous comment box, but he set some parameters.  He had all of the junior officers and NCOs participate; this was not open to the rest of the Soldiers.  We each wrote down strengths/weaknesses of each individual (including ourselves) and placed it in each person’s patrol cap.  Once complete, each person read what they thought their strengths/weaknesses were and then read what their peers wrote.  We had a healthy discussion about what we read about ourselves and were able to talk through with each other ways we can sustain/improve.  I thought it was eye-opening and effective if done properly.