The most important thing for artists to keep in mind about Social Media is that someone else owns it. Someone else makes money off it, someone else ultimately controls the content. So for artists, the goal is to get people off Social Media and onto your media. quickly and reliably.
Definitely, engage people, be sociable, leverage the internet -- but do all of that through your channels, your platforms.
Social Media is a business model that makes money off the people who use it. Facebook users who get offended about privacy invasions are very naive (and also cute). Zuckerberg literally founded that company on stolen personal information from fellow Harvard students, but in 2010, that's just a colorful anecdote, right? Business is like that.
We're all just numbers on a spreadsheet to the men and women who run these companies. So my only advice to artists today is this: don't let them use you without using them at least five times harder. Social Media is where you advertise for free -- not where you do business.