The crooks don't leave a detailed itinerary. For some people that doesn't matter. But for someone in an abusive relationship, for example, it's dangerous. It will take effort. Any conflict will end up in the Supreme Court going up against the First Amendment.
Employers have broad rights of surveillance since it's their facility.
But employees still need to address the issue of the law. A real interesting case came up recently. Employers have been sued by their employees for reading their email, as I'm sure you've heard, but there's been a case of employers being sued for not monitoring their employees' mail. Racist jokes were going around the office on email and the employees said the company should have been aware of this. So these cases are hardly ever clear cut.