I tried it for a few months in grad school. It works better than you'd expect, but not as well as you'd hope.

Days 2-3 were very rough, but after I acclimated, my subjective experience was similar to staying up a few hours past my normal bedtime (mild fatigue, but not unpleasant or debilitating if I was actively doing something).

Three things killed it for me:

1. It is very difficult to maintain a social life if you need to go home and nap every 3.5 hours on a strict schedule.

2. My class schedule was different on different days of the week, so I had to fudge my nap schedule around the classes. The fatigue was much worse on the days (Tuesdays and Thursdays, I think) that I couldn't keep my usual nap schedule.

3. Any stimulants at all will wreck the sleep cycle, and weird sleep cycle or no, I often find myself needing caffeine in order to acheive the mental energy I need to force myself to focus on something I need to get done.

As for formal experiments, the best source I know of is "Why We Nap: Evolution, Chronobiology, and Functions of Polyphasic and Ultrashort Sleep" by Claudio Stampi. It documents most of the existing studies as of when it was written (1992) as well as a formal study conducted by the author. It's out-of-print and fairly rare, but there's a PDF available here: http://sleepwarrior.com/Claudio_Stampi_-_Why_We_Nap.pdf

I managed polyphasic sleep for a week once. It was hellish awful, and eventually I couldn't force myself to carry on through the barrier and see if it lifted...

It doesn't seem like anyone really keeps up uberman for much longer than a year.

An alternative sleep schedule that I do sometimes is biphasic, 3-5 hours twice a day.