A great resource for all things sleep-related is the book Sleep : A comprehensive handbook by Tefilo L. Lee-Chiong. In it - and elsewhere, although I don't have the links in front of me - free-running sleep is a type of CRSD (Circadian Rhythm Sleep Disorder). Not necessarily a bad thing, but certainly unusual.
Personally, I've never tried it with any sort of boundaries or note-taking, but it only seems to work for a week or so. I've never tried - nor would I think I'd be able - to sustain it indefinitely.
Out of interest, what are your current sleep schedules like?