Social media can of course be employed in business-to-business markets too. Not only for marketing but much more importantly for product development and for the improvement of workflows and information processes. Businesses can actually include social media functionalities into their products as well as build products around social media platforms.
The potential of employing social media platforms for any sort of information flow is fascinating: eCRM, social CRM, workflow management, closed company social networks, project management are just starting points where companies have found out how to gain efficiency by relocating communication processes to social media platforms. Security is certainly a concern, but can easily be controlled.
Here are some examples of b2b brands that have used social media for marketing or as a product/service feature:
T-Systems
Sun Microsystems
SiemensPLM
Intuit
EMC2
SonnCom Marketing Blog 