I don't know about the M&M's but has anybody in phase 2 tried the Pistachio Bark recipe yet? (pg 241 in the book) It's made with semi-sweet chocolate and roasted pistachios. It sounds wonderful for that "I need a taste of chocolate" feeling.
If you have ventured over to the Prevention board, you have probably gotten the impression that Peanut M&M's are ok. There seems to be a lot of discussion about that particular treat on the boards. Additionally, the glycemic index in the book has probably contributed to that as well, as it rates Milk and peanut M&M's the same.
My thoughts on the M&Ms question. They have a lower glycemic index, but GI is not the only criteria that we should be using to decide if something fits into our eating plan. GI only tells us how quickly a food will make our blood sugar and insulin rise. I'm not sure, since I don't have a bag in front of me, but they probably contain a lot of saturated and/or trans fats, and don't have a lot of nutrients.
Now, having said that.....they are one of my favorite food groups, and one day I hope to be able to taste them again.....if I can control myself enough to eat them in "moderation".