There are a lot of folks who see social media--facebook, twitter, blogging, plurk, friendfeed, and more--as an opportunity to promote their businesses. I have this advice for them:
Social media is about information. If the information is valuable and interesting it will go viral. If it's transparently commercial and self-serving, it will not. In fact, it may have the opposite effect. I mentioned that in a conversation with my lovely wife and she said, "Write that down. Now."