> Even if the company has a rule that you're not allowed to use it for personal things, the law supersedes that and you still can't do it willy nilly.

Companies are not homogeneous blocks of matter and there is always information some people at the company may need to know that others have no business dealing with. Tax, banking and health related information are some of the things that I can think of that would be shared on a need to know basis with people at work and have no business to be seen by people outside of the intended audience.