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All great questions and oftentimes unanswerable because the platform is still so very new.
One individual I have been following for a long time is Chris Brogan. He writes an amazing blog that extensively covers how to use social media and social networks to build relationships and deliver value. You don't want to miss it.
And this post, 50 Steps to Establishing a Consistent Social Media Practice, is one of my all-time favorites. It serves as a primer to getting your arms around social media.