I'll come out and say that although I haven't used amphetamines (though I know the story of Erdos as well as the military using it), I have been prescribed valium for anxiety issues. It's helped with random things in life like striking up conversations with completely random women at bars by reducing the anxiety felt in a situation.
Anecdotally I know in the SF startup scene, amphetamines are used quite a bit. Amphetamines (of which adderall is one) are basically a better version of caffeine. It allows you to stay up three or four days perfectly lucid (unlike the stress response from caffeine from increasing cortisol levels in your bloodstream), and you also get a mental speedup (quite literally, the clock speed of your brain is increased)
Anyways, I really hope they legalize this stuff someday hah! I'd be a lot more productive, especially with reading the laundry list of books on my reading list...