I like where this thread is going - does social media convert to sales?
For our production company, we did see direct sales coming from YouTube. Since we created a channel, the prospective client saw our animations and gave us a call. We always route our YouTube channel back to our site, so it makes it easy on the client to find us.
For our training & books, it has been more branding and/or indirect sales. Our Twitter feeds keep the flow of jobs, news & tutorials. This keeps our readers interested. We get responses, answer in a timely manner & those lead to fans. From there, I find those fans either purchase and/or let others know about the information. At the end of the day, if the info is useful, people will sign up.
One thing I didn't see mentioned about social media is the conversation between client & "fan". For us, this has been very helpful in planning future events and staying current with the trends. For example, we recently asked on FB if people were going to Siggraph this year. Most of our network of people said "no". That information, combined with our internal marketing / analysis, concluded we should not go this year. While it didn't make a profit, we didn't potentially lose a lot of time / money.