As an employer, I have never done this and would never do this. The entire approach signals that the company has no faith in itself or in its hires. As a potential employee, I would certainly decline to work for a company that did this -- not because I'm looking for a place to "hide out" and be a slacker or something, but because I don't want to work at a place that shows that level of disrespect/mistrust, or where I'd have to be constantly looking over my shoulder.

On the other hand, I have always used probationary periods when hiring people, and I have no problem accepting positions that come with a probationary period. As a hire, I really appreciate probationary periods because they cut both ways -- if I discover that I don't like working at the company, a probationary period lets me leave without it harming my career.

But none of those companies (including my own) that used probationary periods felt the need to indicate in advance that they don't have even a basic level of trust in people.