Consider too, an internal wiki for capturing company information and processes and documenting knowledge which would otherwise be lost?
Social media can certainly and validly be an internal exercise as much as an external one.
Even so, you still should give consideration to your outside audience. You may not want to, or be permitted to, talk about the company itself. That doesn't stop the company from talking about the industry it is in.
In fact, having a company blog about just general industry matters can be key in pitching yourself as an expert in the field. When people use search engines and increasingly find themselves coming to your company blog, you will garner a deserved reputation as leaders in that space and someone whose products and services should be sought and trusted.
Put social media on the agenda. Does your company have a social media strategy? If not, it's time.