What is the biggest risk in social media?

I've led and been involved with various social media risk assessments.  It is a worthwhile exercise for any business, and should be reexamined on a regular basis.  One critical element is assuring that the assessment has equal focus on the benefits and the risks associated with social media.  Everything has risk.  The assessment needs to determine if the benefits outweigh the risks.  In many cases, the business will decide to accept the risk based on the perceived value.  Of course, risk should always be minimized by identifying and executing mitigation activities.

The biggest risk that repeatedly arises is the risk of not participating.  It's different that all the other risks which have a direct cause and effect.  This risk is having an effect due to inaction which could lead to loss of relationships and market share to competitors.  The impact is hard to quantify, but can be significant.  The mitigation for the risk is a tough one, since it involves culture change from the top.  Senior executives need to be convinced that there is a risk of not participating.  If companies don't recognize this risk, they may find themselves lagging the competition. 

What risks have you seen for your company? I'd be interested in your insights.