Newspaper!...
The usual culprits I suspect are Noise, vibration, harshness and lighting. In the 340 this seems to be reasonably well addressed, with some more thought on designing a seat that is durable as well as comfortable. [how long does the lumber support remain "adjustable"?] Also 340 specific is the horrible selcal/cabin "chime". This always wakes me from the bunk! A better designed cockpit/bunk arrangement could reduce fatigue by allowing adequate inflight rest. This includes the cockpit door [post 11/9 mutha] closing arrangement, galley and toilet.
-sorry moved a bit from the flight deck there.