I've been tracking my food since the middle of January. I always thought I was a pretty healthy eater consuming lots of fruits and veggies, only whole grains, very little meat. Once I started tracking what I was eating, I found that on the days I ate more protein, I felt more satisfied and didn't think about snacking as often. Recently I've noticed that I seem to have more energy when I include protein in my snacks.
Thinking more about this, I really do notice a big difference in husband's moods since he's been snacking mainly on proteins. He's less moody, isn't bothered as much by the little things that happen in a typical day (people cutting in front in grocery store lines, etc.), and in general, just seems happier.
Although I've consciously cut calories to drop some weight, I think adding more protein to my meals and a bit to my snacks too, has helped me lose weight at a faster pace then I've been able to lose it in the past. I know myself well enough to know that I'll always prefer even simple carbs over most proteins, but I'm finding that protein really plays an important part in both physical and mental well being.