A Northwest flight was in the news recently when it overflew its destination by about 150 miles and the pilots didn't respond to air traffic control. It turned out that the pilots were working on their laptop computers (against airline policy) and got so engrossed that they missed all the attempts to communicate with them.
I don't want to dive into all the hand-wringing over this incident (which ended without damage to anything other than the pilots' professional reputations and credentials). Others far more qualified than I have weighed in on what a terrible lapse of judgement this was.
But this does highlight what I see as potentially an increasing problem in modern aviation: complete and utter boredom.
Over the past 20 years, cockpits have become more and more automated, and modern airliners literally fly themselves with almost no intervention from the crew. Even 4-seat propeller planes of the kind I fly are becoming more automated--it's getting hard to buy a new airplane without a complete digital instrumentation system (aka "glass cockpit") and sophisticated autopilot.
For the most part, this is a good change. Computers are much less likely to make mistakes than people in the routine operations of the aircraft, and can navigate far more precisely. The job of the human pilots is no longer actually flying the airplane, but communicating with the ground and being ready to take over in case something goes wrong (which it almost never does).
The downside is that it leaves the flight crew with very little to do during the cruise phase. If you think it's boring sitting on a 4-hour flight, imagine what it's like for the pilot and co-pilot. They are required to sit in their seats and be alert for hours at a time, but not permitted to sleep, read books, play games, or do much of anything other than talk to each other and (very occasionally) ATC. Even standing up and going to the bathroom is actively discouraged for security reasons.
This sort of enforced inactivity plus alertness is simply not something human beings are good at. The amazing part of this incident is not that the pilots got sucked into some other activity, but that it doesn't happen more often.