You can see "who" you are by typing "w" or "finger"...it'll be obvious. As far as the "phantom" users, I get that too. They won't disappear when logging out and back in, and I don't reboot (although I'm dying to try iTunes2). :D
"w" output:
[level9:~] level9% w
1:32PM up 9 days, 12:26...