Are you are Using Social Media as a Prescreening Tool?

Many companies are starting to use social media to prescreen their applicants. You can gage whether the employee is presenting themselves as professional, see their communication skills, will their personality fit the organization, do they make mention of drug/alcohol use, etc. Many employers see this type of prescreening as a helpful tool in finding the right candidate, but is it a good idea? By using social media as a prescreening tool could you be setting your company up for a lawsuit?
First, let us make mention that LinkedIn is a social media outlet that is used to present your professional experience to others. Notice that nowhere in a person’s LinkedIn profile does it make mention of you marital status, religious beliefs, or sexual orientation. The reason for this seems pretty obvious..if it is a social media outlet for a professional purpose that information is not pertinent.
Now let us take a look at other social media outlets such as Facebook. Facebook is clearly intended as an outlet for you to be yourself. You do post your marital status, your religious beliefs, your sexual orientation and other personal information about yourself. If you are a company who is using Facebook to prescreen your applicants you are able to see information about a candidate that you would NEVER be able to ask in an interview. Would you change your mind about a candidate if you knew that they had five children that they care for solely? What if you learned that they are homosexual? What if you learned that they are a swinger or in an open relationship?
This sounds like it could be a rising legal issue and some companies may find themselves in hot water doing this type of prescreening. Any thoughts?