I have a not-quite-two-month-old baby so I think about sleep a lot these days. She actually isn't all that bad a sleeper as these things go but a good unbroken 7-8 hour stretch is now a distant memory for me.
I also happen to be re-reading LOTR at the moment. I realised the other day I'd not read it in a few years so I dug it out for the, what, 10th time? In the early chapters as Frodo and his friends cross the Shire sleep features quite heavily; camping outside, marching at night, finally getting a proper rest at Tom Bombadil's house, etc.
Anyway, it amused me to think of how blithely sleep is treated by most D&D players. Night comes and they glibly decide "Boris is on watch for the first 3 hours, Gwendolyn for the second, Job for the last" or whatever and that's that. The cumulative effect of broken sleep (especially when there is an encounter as there often is), the fact that you never sleep all that well in a tent, the fact that dawn comes *really* early for much of the year... We just ignore it and get on with killing orcs.
People have come up with interesting ways to make encumbrance, rations and so on easy to keep track of. Is the logistics of sleep deprivation the last frontier? (Don't look at me for ideas - I got 3 hours, then 2 hours, then 3 hours again between 9pm and 7am last night. I'm hardly in a position to make up D&D subsystems.)