I attempted the Uberman sleep cycle about a year ago. I managed to get by with 20 minutes sleep every 4 hours. I lasted 2 weeks before bad things started happening (hallucinating, extreme weakness, and major cognitive deterioration). It was a fun experience but something I am convinced is fabricated and doesn't work despite some peoples anecdotal evidence.

Eventually I ran into this blog and when I read it I immediately quit the cycle http://www.supermemo.com/articles/polyphasic.htm

If anyone has any questions about it/are thinking of trying a sleep cycle I would be glad to answer!