This news article is older than required. However it is a very relevant article which highlights a social and ethical issue. It also contains information that still holds true and is relevant to the discussion.
Interesting article that gives a good overview of employment concerns. It is a little unbalanced in the sense it does not offer the other side of the story. But this makes it a good starting point for discussion
"Lack of focus on social networking can expose organisations to a variety of risks, including loss or leakage of information, damage to a company's reputation, illegal downloading of printed material, and identity theft,"