Interesting... I just started a biphasic sleep schedule (4.5 hours of sleep from 1:00 to 5:30, and then 1.5 hours of sleep from 19:00 to 20:30) but now I'm wondering if the cost will outweigh the benefits.
I've done a 6 and 2 biphasic schedule (or sometimes 7 and 3), and I felt better than I ever had before. It's difficult to fit the nap in with work though.
I think in many ways the "Italian" sleep schedule (up at 7, awake till 2, sleep till 5, awake till 2) is very natural. It's no less sleep, but it feels more refreshing somehow.
Depending on where you live, the hottest hours of the day are usually between 12 - 5. Maybe it's instinctual for predators to not want to do stuff during those hours?
Biphasic sleep schedules are arguably the default setting for non-industral society humans - http://en.wikipedia.org/wiki/Segmented_sleep - and while it appears to have benefits in terms of mood and alertness, it may not be entirely healthy as a way to reduce the total amount of sleep if you need more.
Biphasic is fine, sleep deprivation is problematic. You've got a grand total of 6 hours, when most humans do best on 7-8, so you might be running a bit low.
I think in many ways the "Italian" sleep schedule (up at 7, awake till 2, sleep till 5, awake till 2) is very natural. It's no less sleep, but it feels more refreshing somehow.