Allow only one login per username

[Floris]

I think I saw in the admin control panel a option to give a user an IP address. If I think it is what it is, you can restrick the username by just that ip or range. Maybe that helps.

I dont know how currently, but i think it is possible (that is, if the above scenario is so) to code-hack a little bit (or even template hack) something so during registration it will note the ip through a hidden-input field and store it, so when shared, others can't use it. (automation means that you have to accept ranges though) - not everybody has static ip.