Good question. Excluding fuel leaks, mechanical and rock/hard place situations, probably a lot of them. Ever notice how many of those are 'crashed within 3-20 miles of the destination'?
I often wonder if the fuel exhaustion issues are a direct result of ingrained automotive driving habits. Driving range is fairly reliable for x miles to a tank so reset the trip meter and you're good to go. That works fairly well for aviation too...Same number of airmass miles per tank HOWEVER all else being equal, with a headwind the airmass is moving backwards away from the destination thus requiring more airmass miles for the same ground distance.
Then there's the fun game of jumping from one rental to another and sorting out their actual fuel load and actual fuel consumption. It's near impossible to find a rental with a reliably calibrated tube to stick the tank with that you feel comfortable using.
Where I come from:
XC lesson #1: Measure fuel as units of time. Distance is totally irrelevant. When the timer goes ding, land and refuel now, not another 30 miles along...
XC lesson #2: Impatience/inconvinence range: Plan your last fuel stop >= 45-60 minutes from the destination, anything closer is asking for gethomeitus since you're already almost there.
