I've always been a night owl and late sleeper. Most of the jobs I've held in my life were night jobs. Yet I've often been subject to criticism from early birds for being lazy.
Today I feel vindicated. The Week magazine reported on research which discovered that we night owls maintain our alertness levels much longer than early birds. At 90 minutes after rising, early birds and night owls were equally alert. However, at 10.5 hours after rising (afternoon for birds, evening for owls) night owls were much better able to maintain their ability to focus and react than early birds. In short, night owls can be more productive towards the end of their day than early birds towards the end of theirs.