Found this article on Wired. Good reading, although rather frustrating.
There are millions of cover songs on YouTube, with around 12,000 new covers uploaded in the last 24 hours. Nearly 40,000 people covered Rolling in the Deep 11,000 took on Pumped Up Kicks, 6,000 were inspired by Somebody That I Used to Know.
Until recently, all but a sliver were illegal, considered infringement under current copyright law. Nearly all were non-commercial, created out of love by fans of the source material, with no negative impact on the market value of the original.
This is creativity criminalized, quite possibly the most popular creative act that’s against the law.
Read the article: Criminal Creativity: Untangling Cover Song Licensing on YouTube – Wired