It's amazing how similar they've remained.
New World monkeys broke away 30+ million years ago, and yet despite the time, geogaphic distance, and climatic changes, they still look like monkeys. Considering the changes that happened to whales, porpoises, elephants, and other species over roughly the same time period, I find it fascinating.
BTW, I was just wondering how those groups migrated out of Africa. Their mobility on the ground isn't very good.