I maintained a semi-uberman sleep cycle for about 2 months during college (I was Alex_Altair's polyphasic-buddy, for my second attempt). I slept for ~3 hours a day during this time. We spread it out into four 30 minute naps. The transition period took 3 weeks for me (I believe Alex_Altair did not successfully transition, and we abandoned our team effort, but I continued on my own). I would sleep through my first class each day (approximately 50 minutes) and then maintain the sleep cycle properly for the rest of the day. I eventually screwed up sleeping on the weekend (by consciously choosing to oversleep) in a way that resonated the rest of the cycle until I wound up back in monophasic sleep.

Would I do it again? If I had enough time to transition, and a schedule I could set myself, yes. It's probably been long enough since my previous attempt that it seems like a good idea to try again (where what I remember of the transition period is mostly tainted by nostalgia). My natural sleep cycle is somewhat stupid, desiring 10 hours of sleep a day and advancing independently of the earth's rotation, so reducing that to 3 hours a day and having it synchronized with the earth is a major benefit.