According to a survey conducted by CareerBuilder:

• 45% of employers check social networks before hiring
• 11% plan to start use social networking sites for screening in the near future
• 35% of companies had rejected a candidate based on information from a social-network profile 

What does this all mean?  Social screening is increasingly becoming integrated into the pre-employment process.  With that being said, both candidates and employers should proceed with caution as we figure out the best ways to access and use available data in practical, legally defensible and ethical ways. 
 
Employers:  Using social media for screening and background checks can be a very powerful tool, but it is far from being risk-free.  Hiring Managers, HR Professionals and Recruiters should keep in mind that the traditional rules still apply in the Digital Era (i.e. anti-discrimination laws).  In fact, with more and more cases of mistaken identity, fake accounts and inaccurate information popping up, you can be sure that a host of legal risks and compliance issues will come knocking at your door.
 
Candidates: This is simple.  Use common sense and avoid blending your personal life with your professional life.  Check out The Tweet and The Response for a great little cautionary tale.