Interesting. I decided to do some research and there are a few cycles so it really depends on what you do. The best one I saw was called the everyman cycle. It involved one three hour sleep period and three 20 minute sleep periods throughout the day. I also read that this is best used when not switching to the uberman cycle right away since the uberman cycle is the toughest cycle and doesn't allow any prolonged sleep periods.
There is one semi-famous guy (bucky fuller) who achieved the dymaxion cycle, which is 30 minutes every 6 hours. Doctors examined him and found him healthy. He was also an extremely successful businessman. It was his business that stopped him since his partners persuaded him to switch back to normal so he would be on the level of a normal human being (none of his business partners could do it). Despite being well known there is no real proof that he actually used the dymaxion cycle, although a time magazine article in the late 40's wrote about him.
The main idea behind all of this is being able to get into rem sleep faster without the other parts of sleep which are a waste of time according to the theory. In order to do this you try and get into having extremely lucid dreams (a sign of rem sleep). Yet as no one really knows why we sleep to begin with there are a lot of issues with this idea. We only know sleep is necessary and rem sleep is the most productive part of our sleep cycle. Whether this method really works or not is still up for debate.
There have been numerous tests from both military institutions and bloggers. Military claims it is a disaster after so many days. Bloggers all claim it is a good thing, but most of them are persuaded by a wife or some other person to switch back to the normal cycles of sleep for the sake of being on the same level as anyone else. Almost no one makes it past a few years. Also you can not change your nap periods very much so it can ruin your schedule and requires a stay at home job or very flexible hours. You are sacrificing flexibility in your schedule for increased hours. Also be prepared to spend many of those extra hours alone.
I hope this helps shed some light on this issue.
Sources:
http://www.highexistence.com/alternate-sleep-cycles/
http://www.highexistence.com/six-tips-a ... sic-sleep/
http://en.wikipedia.org/wiki/Polyphasic_sleep
http://www.stevepavlina.com/blog/2007/0 ... ear-later/