Frugivores eat only fruit, including a few nuts, tomatoes, and avocados, as well as sunflower seeds. Their reasons stem from ecological (fruit falls from a tree, and the plant need not be destroyed to provide its meal) to health-related, and frugivores claim they feel lighter and full of energy than they ever did when they were eating the typical omnivore diet. Critics worry they'll become sugar addicts, and the diet is obviously missing a few things (complex carbs, for one), but the frugivores quoted in the article say they're healthier than they've been in years.
Personally, balance is an important part of my diet, so going fruit-only would never work for me. What about you?