The person interested in your business, service or product doesn't want to just observe it from the outside. To become a true brand advocate and spread the word - to become a part of your tribe - they need to be a part of the conversation.
Social media provide the best platform for that conversation to take place. You can tell your fans about what is going on and most importantly, get their feedback. You can find out what features they are looking for. What benefits they need. What color they want. It's like the best focus group, and you don't even have to cater it. All you need to do is be brave enough to start the conversation, be prepared for their feedback, and be honest with your faults. Consumers aren't looking for perfection, they are looking for truth. You must be transparent if you want to be believable.
This article "Facebook Do's and Don'ts" by Evan Garber provides great tips on how to best utilize Facebook.
You have to participate in the conversation about your brand - otherwise they will just talk about you behind your back.