One sort of alternative sleep schedule I've practiced on occasions that enables me to get more active hours for a few days in a row without being too sleepy is going to bed later and later each day and sleeping fewer hours than usual. Normally, if I go to bed at my usual time and wake up after, say, five hours, I'll be sleepy, irritable, and unproductive all day, and after a few days of sleeping less than 7 hours or so, I'm good for nothing. But if I go to bed very late and wake up sometime after my regular waking time, I feel much better, so that constant pushing ahead of both bedtime and waking up time enables me to sleep much less for several days while feeling tolerable.
Of course, this is practical only when working on projects where you don't need to coordinate with others. Also, it probably wouldn't work for many other people, especially those who become extremely sleepy late at night, and who wake up easily and full of enthusiasm in the morning. (Whom I envy -- I always find it hard to fall asleep in the evening, getting up after less than ~8 hours of sleep is for me sheer torture, and after waking up I'm slow and sluggish for at least an hour.)
My sleep 'schedule' is something like this, in practice. I go to sleep when I'm tired and get up when I wake up and am no longer tired, without worrying about the clock at all, and I've been doing so for 2 years now. My days usually last between 23 and 28 hours, and seem to run longer, not shorter, when I'm stressed or busy, both in terms of the length of time from the start of one sleep to the start of the next and in terms of the awake:asleep ratio.
My friend and I are starting the Uberman sleep schedule (six 20-minute naps spread evenly throughout each day) tonight. Have other lesswrongians experimented with alternate sleep schedules? Are any of you qualified medical experts who can give input or advice? Success stories and failure stories would both be appreciated, and I'll keep you guys posted on our progress.