Have to echo the comments, but would say the main reasons are the factory rear diff., bad tires, 4th to 5th shift (into 3rd) but mostly bad drivers. People think that just because their SUV or whatever pick-up or daily driver car comes stock with 400+ hp, they can handle 400HP, 450HP, 505HP or 600 HP in the Vipers. Different power, though the HP numbers are the same.
My personal experience with the Viper is the factory rear diffs are the main headache. A car with power and throttle characteristics like this, requires a Quafe type of diff. Everything to both wheels.
Tires; the Run-Flats on 03' to 06' are very poor tire. The rubber is just too hard, hence traction is way down, PS2s are noticably better. Tranny, I don't know what it is about that 4th to 5th shift but I personally have to get my body in the same position and tighten my arm like a falcrum to shft from my shoulder, if I am trying to shift aggressively otherwise if I pull it slightly, then I am in 3rd gear. Learned to just make sure I do not dump the clutch after that shift because if you ease out on the clutch and hear and feel it really winding up on RPMs, you can quickly push it back in and reshift it again, slowly into 5th.
Lastly, hark back to the days when you were 16 years old and your parents did not want you to have a Sports car with lots of power because they feared you would "wrap it around a telephone pole". Same principle here, as the car and the power have to be respected and the only way to do that is to ease into it a little more each time and learn the car and learn about yourself.
I have owned mine for over 4 years now and while I am much more comfortable with my skills and the car now, I know my limits. When I first got it new, it scared the daylights out of me and I had been driving 600 HP Saleens, 550+ HP Custom Trucks, supercharged Mustangs and muscle cars of yore. Viper is different, but like Arby's says "Different is good".
Well worth the patience though.