ok, let me set you straight.
I love numbers so here we go.
1. netstumbler just locates wifi AP (access points) and lists their SSIDs. SSIDs are not passwords, just network ID. It detects APs by an active method - it sends out a beacon that wifi AP respond to with their beacon (the SSID). APs that are set _not_ to respond will not be detected by netstumbler. You'll need a passive AP detector, one that sniffs for signals of traffic, use your search engine.
2. wardriving is personal, you might enjoy sitting at home, but I like finding cool places to hang out, and I do have a nice car. It is a personal curiosity that drives me to map out wifi APs, not nessarily a need. I guess I am no different from that bum that likes to go through your neighborhood's garbage cans, sometimes he finds some neat stuff. It is an obsession/compulsion. And it keeps my skillz up.
3. Read the forum for discussions on wifi, the answers to your questions are there. It is rude to ask questions that have been asked recently.
4. Since ignorant people have setup their own wifi routers, they did not change the default passwords. Netstumbler will tell you the brand of router it is, and you would consult (previous discussion on suck-o) this list for the router IP and password;
When I connect to unsecured wifi AP, I check for default logins. I can enable logging to track all incoming and outgoing TCP traffic, browsing logs, and even set a email for it to send the logs to. If you lock out the owner by resetting the default login, usually their only recourse is to use a paperclip to hit a reset/reboot button on the router - therefore erasing the evidence of your trespass. You now ownz it.
5. Aircrack? Have you read on how it works? It needs to collect about 600,000 sniffed packets in order to decode the WEP used. You'd need a heavy traffic wifi AP, like in a corporate site, to generate enough captured packets to crack. You don't want to sit on your neighbor's family wifi AP for 3 years do you?
6. If your AP is open, you are letting anyone in your neighborhood come in to your house, anytime they want. They could d/l a movie and lag your network, or d/l kiddie porn on your ISP account. You might as well let strangers use your car to rob a bank or kidnap a child, its the same thing when the police come knocking on your door, because they got your car's license plate number at the crime scene. On the reverse side you can sniff that traffic easily for their passwords and personal nfo, even email logins. When you connect to a 'free, unsecured' wifi AP, expect no privacy, and avoid stuff like banking online.
7. security is in the form of encryption, avoid protocols that send nfo in plaintext. https is a secure protocol for webbased transactions, don't send CC or personal nfo over http. Use tools like ScatterChat to encrypt IM convo, send your sensitive email only after it has been encrypted on your box. Don't worry about your suck-o surfing or IM to your girlfriend or emails to mom, you are not that important enough for compromise.
DNR