and what impact will it leave in the future? positive or negative?
Yes, social media provides new marketing methods and all, but then again, most of the entertainment business' revenue comes from advertisers. so, social media might be an ally and an enemy at the same time.
and i dont believe selling DVD's or songs help, as final customers tend to find ways of getting them for free. and making laws and regulations against it will hurt the relationship between the suppliers and these final customers.