Ok, I think I can stop posting about my biphasic sleep experience, unless something special happens. It's my 14th day as a biphasic sleeper, and I think I'm done with the adaptation phase so I'll just relate how it changed my life.
Today, as opposed to my monophasic sleep period, I feel much more refreshed, and have no problems waking up in the mornings. I used to have 3 different alarms to wake me up, and felt tired all day long. Now, I may be groggy for 10 minutes if I gave myself too much or not enough time to fall asleep (and the alarm wakes me up during a sleep cycle), but I'm in an excellent shape the rest of the day; the only times when I'm tired means it's time for me to go to bed.
I now clearly remember dreaming, usually after my core sleep (even though I sometime have weird dreams :). And I'm often hungry when I wake up (?).
My biphasic sleep's schedule is relatively flexible, and I don't have to fall asleep and wake up at the same time everyday (even though I try to be regular for practical reasons). One of the rare penalzing aspects of biphasic sleep is that I'll be really tired if I miss a nap (maybe it'll be different in a few weeks, I'll let you know), but it's just like if you don't get enough sleep when you're monophasic.
I have a lot of extra-free time I can use, since I'm alert all night long: I can work until 2:00 AM without being tired; biphasic sleep also increases your productivity, and I'm often inspired when I write an essay, or during a math test, etc... (better grades).
The only real negative aspect I can think of is that it may mess up your social life. But if it doesn't, give it a shot; it's worth trying, trust me :). Try to keep a regular sleep schedule, at least the first 2 weeks so that your body adapts fully and easily. Here's a great site if you want to try biphasic sleep.