comScore published a study called "The Power of Like" which has a nice chart to keep in mind when teaching brands the basics of social media marketing. I think this basic view works well, but any social strategy needs to keep in mind the different types of fans. Some are HUGE, some not so much. Is Facebook better for your superfans or are there other ways to reach them (that won't alienate your more casual followers?)
What if Twitter sellers all blew through their sales goals? What if Twitter didn't innovate their ad strategy? I envision a more robust brand page developing arming brands with powerful ways to attract and engage audiences.