I think a vegan diet requires a lot of work to really make it a balanced diet, I don't think I could ever do it.
My brother did the paleo diet for about a year, he lost weight while he was doing it but for some reason he stopped and seems to have gained back everything he lost. But I can't say he did it very well, he considered a steak and an orange to be a complete meal! LOL
I really try to make my meals really balanced and full of "real" food, I used to follow the South Beach Diet religiously before I had kids but I find it hard now. I eat a small amount of dairy and have started using olive oil a lot, which comes from the Mediterranean style diet.