I saw this article about employers using the web to disqualify candidates. There isn’t much depth there, but it shows a serious perception problem that a lot of people have.
I honestly think that the writer has a deep misunderstanding of the concept of rights and responsibilities. Yes, you have the right to say what you want, but it’s tied to the responsibility that you stand up for what you say. For example: if you put up a blog that makes constant threats against someone, shouldn’t you be held accountable for those threats? For a more relevant example: If you put up a blog that constantly criticizes Microsoft and threatens to steal code from them, doesn’t the beast of Redmond have a right to know this when you apply for a job there?
If you are arguing that a potential employer shouldn’t know about that nude picture of you that got taken over spring break, you are still wrong. It is your responsibility to make sure that pictures like that don’t get out into public. In the past, that kind of thing would get publicized by sleazy journalists. Nowadays, that kind of thing gets published straight to You Tube. Same problem, different media.
There are times when being investigated by an employer is actually doing you a service. If you are going for a job that requires a security clearance, you should expect to get screened. All they are really looking for is a reason why you would be denied the clearance that is critical to your ability to perform the job. If you are going for a job that requires you to be a public representative of a company, they need to make sure that you don’t have any secrets that could damage the company. If you are applying for a job with a political organization, you deserve to be investigated. In every one of these examples, the employer is looking for something that would have gotten you fired anyway… possibly after a great deal of public shame.
In general, I doubt that it is a common practice to investigate someone without a pressing reason. Having been on the employers end of this scenario in the past, I can tell you that investigating someone’s political opinions, spring break habits, sexual orientation, or any other irrelevant tidbit is prohibitively expensive. It requires time to dig these things up, and there just isn’t enough bang for the buck here to make investigations useful.
As a final point, why would you want to work for an employer who uses irrelevant information to determine whether or not you should be hired? Really… you are better off somewhere else anyway.