Currently there are just way too many things that could go wrong when going from one supercharger to another. You could look at the navigation and see you need 180 miles, so you charge to 190 miles. But going to the Supercharger is uphill, but you don't know it. So it actually takes 200 rated miles to get to the next Supercharger. But you don't know that because no where on the Model S screen does it say that. So, either you slow up to like 55mph and pray/hope that you make it (now that's range anxiety) or you drive normally and get surprised when you only have 20 rated miles left but you have 30 miles to go. Then, you freak out and see if there's a hotel you can crash at within 20 miles, but if there isn't then I don't know what you do.
The Model S (and future cars) really should be dummy-proof. If you have a Supercharger as your next destination in navigation, then it really should make it next to impossible for you not to reach the next Supercharger. It should make sure you leave with enough charge and if you're using too much energy (ie., going too fast, blasting A/C, etc) then it should tell you exactly how fast you can go and what A/C setting you should use. And if you get to a place where you don't have enough miles to reach the next Supercharger it should alert you that you're not going to make it and you need to charge somewhere.
Even better, the Model S should know my driving patterns (ie., I like driving 5-10mph above the speed limit on freeways) and then calculate how much charge I need at the Supercharger station in order to make it to the next Supercharger station.
No one should really need to read a manual to figure out how to drive the Model S. It should be as easy as hold the brake and press down on the lever to go to drive, then drive.