Use on 2+ computers

So, I understand that BS 2 allows use on up to 2 computers.

How does this work? Is it simultaneous use? Reason I ask is because I have it on my 2 home machines (1 desktop Win7, 1 laptop Mac), but I'd like to use it occasionally on my work PC laptop during a lunch break, as I typically place my orders for recipes during my break.

Brad, any info would be appreciated.

I define it as one key for up to two installs that you are using on a regular basis by the owner.  For example a desktop and a laptop.  Giving it away to a friend would not be good.  Similarly a third computer would not be allowable.

Thanks,
Brad