Is there any risk in putting social media contact information on your company's business cards?

If the business has invested time (and/or employee wages) into creating and maintaining a "company" page on Facebook and profile on Twitter, then yes, definitely promote those of communication and sharing. (LinkedIn too) As for personal FB and Twitter contact info, that would depend on the business you're in. Sales reps who create personal bonds with customers typically maintain a higher standard (or should) on all their social media sites, therefore that information should be shared. Also, a business could implement a social media presence for all the employees using the business email addresses of said employees. The more your business name is out there and shared, the more chatter, leads, connections, and/or sales could ultimately result.

I think it is essential that every company has a social media policy, stating what can and can't be discussed on social media platforms ( e.g. if they are intending to use their social media to discuss work related topics). The company should only allow you to print your social media details on a business card if your accounts are within the social media policy guidelines.

Seems reasonable enough to me to be considered a risk. I'm not a lawyer but if a company allows an employee to put social profile information on a biz card then that could be considered evidence that they support anything that employee says on that channel.