One homebuilder company used a location based technology, where they had put GPS's on the workers' cars. You could then see on a map, on the website, where all the employees where at the time. I think this technique could be useful for companies in many different ways to help with customers service and interaction. One example could be the ice cream truck company wanting people to always see where their trucks are.
Another company created a small social network of their own on their website, and made it really simple to sign up (just through one click by connecting to Facebook or Twitter etc). The same company is also using an own peer-produced Wiki for their products. If someone asks a question other customers who knows can answer. That relates to what Therese said about wanting to hear opinions from other people (friends or just other customers) instead of only the company's thoughts.
A third company (a restaurant) used another feature I liked. If you run a restaurant or a café you can take reservations through Twitter. The guests will have to follow your account in order to make a reservation. They send you a tweet to make a reservation request that you can then answer and tell if you have free tables or not. By following the account, they will also be able recieve information from the restaurant and that will help market the company.
Other social media features that where mentioned can be found here: