I discuss melatonin's effects on sleep & its safety; I segue into the general benefits of sleep and the severely disrupted sleep of the modern Western world, the cost of melatonin use and the benefit (eg. enforcing regular bedtimes), followed by a basic cost-benefit analysis of melatonin concluding that the net profit is large enough to be worth giving it a try barring unusual conditions or very pessimistic safety estimates.
Full essay: http://www.gwern.net/Melatonin
Nope. A tentative hypothesis is sleep apnea, since my dad had that, but how well I sleep is extremely inconsistent (some nights I get excellent sleep, some nights I wake up a dozen times and am a zombie all the next day) and seems to correlate better with whether I've set an alarm than with any of the factors that are supposed to affect sleep apnea.