In regards to the 10% myth: While it's true that the vast majority of your brain is in use, you indeed only use a part of it for your conscious activities. If your brain was optimized to handle all "background processes" more efficiently, or if the "unconscious" circuits could multitask to divert "power" to conscious activity, your mental potential would definetly increase. In at least that, the myth is believeable.
Nope, the brain doesn't work like a computer, it has no overall speed.
Each set of neurons and synapses have a set task, and whilst this can change over time(Learning and memory) it could not just divert proccessing power to another task.
If you had more then 5-10% of neurons/synapses firing at once, the result would not be an increase of intellegence, it would be a siezure.
To programmers, what would happen if someone decided to make the program run faster, by multitasking every single function/routine to run simultaniously. Would it still work ? NO.
I'm no doctor, but I have worked with neural nets before,Some of the minor details may not be accurate, the the overall result is true
While that is true, you do use all of the neurons in your brain, just not all of them at the same time. If you lose a set of neurons, your brain will try to adapt by diverting other neurons away from their normal tasks to replace the missing neurons, but this can cause all kinds of side-effects, like loss of certain functions (especialy with regards to your personality) or cross-over effects (epileptic seizures, synesthesia or other things) because neurons are to close to eachother.