I know I didn't explain it well last night, it was late and I was tired...
Anyway, in answer to #1) No. It'll be checking for more than two _active sessions_ with a TTL of 17 minutes. That is, if you're on at home and it takes you more than 17 minutes to get to work, your old session is "inactive" even though you're still logged in. The difference is between active use (sessions) and maintaining information, (cookies), the latter are really a mechanism for maintaining state, such as your username and post viewing preferences so you're "recognized" by the system. What we're probably going to do, unless someone has a better suggestion, is allow each user account no more than two active sessions. This is needed because you might walk from one computer to your co-workers and login there (or from home to the library, etc), and if we didn't allow more than one, you'd be locked out. And really pissed off, I'd think.
The need for this is because of rampant password sharing amongst people that don't wanna pay their share. On the other hand, why shouldn't your wife/kids be able to view MO from your account at home while you're at work? If you want them to be able to, leave it logged in and they can, or logout and they can't. Kinda like leaving National Geographic on the coffee table for the kids, and hiding Playboy in the broom closet. ;-)
2) Steve, you have to be moderated down to -1 several times to get the Troll ranking, which is several different people moderating you _down_ twice. I wouldn't worry about it, most posts are going to get moderated up. The only posts that we tend to moderate down (and we do do some, look at the last Pay Now... debate with threshold of -1, which you can set above the posts) are those that make personal attacks or are so far off-base and just plain stupid that they shouldn't have been there in the first place.
Lastly, when logged in, look at the bottom of the top left "Who's Online" box for a link to change your password. If you're logged in, you don't need to remember/know your old password to change it.