The assignment was worth 15 points. If the group score was N, I gave them 4N points to distribute to their 4 members, on the basis of contribution. Most of the groups simply distributed the points equally. Some weaker students took fewer of the points for themselves simply because they asked more questions of their group members, and gave more points to the stronger students. One student immediately pointed out that someone could abuse this method by dominating the group work in order to get more points.
Response is reflective and individual.
Groups learn, then it helps. If so, specify the nature of the problems. No, but I might consider that in the future. There were informal comments made on the course assessment form. Each group member was given an average of the scores assigned to him or her on each item by the rest of the group.