This comes up on HN about once a year. Here's my blog where I wrote about trying it: http://www.pchristensen.com/blog/category/polyphasic/

tl;dr version: - the first 5-7 days are just awful but after that you're not tired - deviating from the schedule (say, staying awake 7 hours one time instead of 4) is devastating - you do feel different and perceive time differently. Kind of like San Diego weather instead of Boston.

Interesting experience, worth a try, I'd do it again in a heartbeat if my home and work schedule accommodated it.