So far (fingers crossed) that has not happened to me. I'd be freaking out if it did!
Alot of people (according to the boards) have been being randomly logged out lately, so it may be a server thing, or maybe

if you're one of those people who never log out, it just does it from time to time?
Starry, I never knew that about the cookies - that they were different! I thought Neo went by IP, but maybe that's just if someone's using an ab, or TNT thinks someone's multi main account cheating (making up alot of "main" accounts on different emails, making np and sending them all to one account).
I know the games used to have your email in the game addy, then they went to dob, now they just have the username and a bunch of numbers - which does change. So how they now check on who's playing games I don't know!
R4chel, I have a friend (known her for over 20 years) who uses my computer for Neo (she doesn't have one, can't afford it)...I somehow figured out how to have her log onto my computer (have XP too)...don't ask me how, I'd never figure it out again. She has her own email and account. We don't have each others' passwords to anything, I don't store any passwords and asked her not to (so we have no way of accessing each other's accounts ... and I have a safer surfing policy of clearing cookies/temporary internet/history after every site visited, which I passed onto her too.