Here’s a relevant survey by CareerBuilder.com that puts numbers to something that nearly anyone in recruitment and staffing has observed or themselves instituted: the practice of using the social networking aspects of the Web to evaluate potential hires.

What that means for those firms, for staffing consultants and for jobseekers is that there may very well be reasons not to hire an individual, reasons that have nothing to do with his or her resume or stated experience – and everything to do with what they post or reveal via the Internet.

Here are some of the reasons cited in the survey for not making a hire, based on what surveyed employers discovered by checking prospects’ profiles and posts on social media sites:

• Candidate posted provocative or inappropriate photographs or information – 53 percent
• Candidate posted content about them drinking or using drugs – 44 percent
• Candidate bad-mouthed their previous employer, co-workers or clients – 35 percent
• Candidate showed poor communication skills – 29 percent
• Candidate made discriminatory comments – 26 percent
• Candidate lied about qualifications – 24 percent
• Candidate shared confidential information from previous employer – 20 percent

What a prospect posts on Facebook, MySpace, LinkedIn or other sites is perfectly fair game for any staffing consultant or HR person who wants to make a comprehensive investigation of an applicant.

There’s also good advice here for jobseekers: the barrier between our “public” and “private” selves is pretty thin on the Web.  The offhand gripe about your last boss that you post today may very well come back to haunt you tomorrow.