LifeHacker has a post abut how to function on just 2 hours sleep per 24 hours. The post is based on an article in Wired magazine. The most extreme strategy they talk about is based on sleeping 20 minutes every 4 hours, or 2 hours every 24 hours.
In terms of astronauts, people engaging in 30 day kayak trips, soldiers, and rescue workers, some of these techniques may well be both useful and necessary. But for most of us, I would hope we would aim to reduce or working hours so that we had enough leisure and sleep!