But technically speaking its still duel clienting and you can't be at both computers at the same time and not be afk on another so it is breaking the tos really and wheather they pay for the accounts or not makes no odds to me,maybe there is a time and a place for duel clienting but not at the expense of others when its a team activity. AMEN
The problem is you can't determine where the line is crossed. Back in better days, it was not uncommon to get together with friends once every week or two and play UO. Being in the same room with 4-5 other people, you can do some amazing stuff over the span of a few hours and have a type of coordination you can't get over Ventrillo or whatever people are using. Even 2-3 people in the same room together can do quite a bit.
If a GM looks at such a group, they will see only one IP since we are all behind a single router, but they could see the different accounts and that they are tied to different people. I still go over to a friend's house or he comes over to mine, and we play together, and we show the exact same IP to the outside world, but two different accounts.
However what if somebody is borrowing an account or what if I play with my spouse or kid? More than a few UO players here play with their significant others or children, and a GM looking at that will most likely see multiple accounts tied to one person, but that's still legitimate gameplay.
And then there is another issue - if you have multiple accounts running in a VM (virtual machine) on the same computer, which I have done quite a bit in the past when shuffling things between accounts or when I found myself in a dead area on a shard and needed a healer or some other form of backup. Both VMs are on the screens, I see everything that is happening right in front of me.
I am in fact at both "computers" at the same time since there is only one computer. I am not afk since there is only one keyboard/mouse, at least no more so than when I am afk when I flip over to a web browser to look something up.
In the end, a GM cannot tell whether I am a person playing 2-3 accounts at the same time, or whether there are 2-3 people playing 2-3 of my accounts at my house.