There are companies that use social media, and there are social companies. Some like Shakeaway and Threadless actually make it part of their business. Others tack it on and wonder why it doesn’t work.

Trust is one of the key factors in peer communications and in top-down missives, as you say. LinkedIn does a good job. Facebook doesn’t. You can build trust through:

Policy/terms: “we won’t send you spam”, “only friend those you know already”

Through identity verification: Amazon’s RealName reviewers, for example

Through culture: a more slippery one, but it involves openness (a company letting bad reviews stay up may find that its loyal customers reply to the review to defend the company) and engagement (social media efforts need to be true dialogues between customers and providers).

Rambling now.