I read an interesting accident report once.....The refueling guy refueled the aircraft (C172 or something) and left the fuel caps off EXPECTING the pilot to check the fuel. The pilot and his mate wandered out to the aircraft, and decided not to bother going flying, so they left again. Next day, after the aircraft had been sat on the ground over night in the rain with the fuel caps off, another pilot came out to go flying. It was a cold freezing morning, and the pilot saw the caps were off and assumed the aircraft had just been refueled. He drained some fuel and everything looked dandy so off they went. 30 minutes or so into the flight, the engine failed and they crashed. Apparently the tanks got a load of water in, which then froze and so didn't show up when the tanks were drained. During the flight the water melted and stopped the engine.
I also read another report along the same lines. Pilot saw aircraft being refueled, didn't check the fuel. Fuel guy left caps off for pilot to check....except he didn't. Took off, fuel sucked out, engine stop.....you get the drift.
On the subject of accurate fuel guages, most new aircraft have accurate fuel guages, and most panel mounted GPS's have a facility where you can enter your calculated duration / range and it'll keep a running tally on how much fuel you've got left.....All calculated of course, but better than nothing.
I'm paranoid about fuel, for reasons best not discussed in public
EA