I think this is going to get very ugly... some law firm is going to get very rich out of this...
I don't think it is appropriate to ever get access to personal information without major justification. I could see the need for certain security clearances - but for a 9-5 job, I think it's wrong.
Where the line blurs substantially - if an employee using facebook or personal email on a company computer. Employers should have the right to review all that goes in and out the door of a business. There's too much risk of fraud and industrial espionage to not review anything deemed suspicious.