The help files address the first question: www.sawtoothsoftware.com/support/issues/ssiweb/online_help/hid_web_cbc_none.htm
For the second question, it depends. If my none option was labeled "I would go without treatment to combat this disease" it's probably a lot easier to understand its meaning then if I say "I would not buy any of these 3 computers." In the former, it has a specific meaning with a very real and tangible outcome (continued sickness, maybe risk of death, etc.). The the latter, I probably don't know what it means (I would not buy a computer, I would go to a different store, I would delay my purchase for 6 months, etc.).