There's a new article (Jacqui Cheng, Ars Technica) basically summing up a truth about illegal file sharing, with evidence for this as well.
All of the big music stores are now DRM-free. Yet the RIAA has feared massive copyright violations with use of P2P software.
What has this led to? People are legitimately buying DRM-free music and using them appropriately and not illegally downloading them on P2P networks. One reason for this is that P2P networks are meant for large files; music files are small enough to be bought and downloaded off of regular sites.
The bigger reason is that people will legitimately buy content online [I don't know how to make "super-italics" for super-emphasis] IF IT IS EASIER TO DO THAT than to illegally download music. Often, DRM-ed music from P2P sites are of poor quality and may not be the full song, whereas legal music is of great quality and is of full length. Now that legitimate music is DRM-free (while music on P2P sites have cracked DRM), people would rather pay for music than get trashy quality for free.
On the other hand, movies have not gone DRM-free as music has. This means that it is easier to get a lower-quality but unrestricted free copy from a P2P network than it is to get a heavily-restricted, very expensive normal quality copy from another (legitimate) source. The movie industry needs to keep up with the times; given that soon files the size of movies will become very small compared to P2P network capacities (like how music is small compared to current capacities), it would be in the industry's best interests to remove DRM from movies and start selling these movies online.
DRM is a solution to a nonexistent problem, and is in the end a bigger problem than the "problem" it "solves".
Sadly, the RIAA and MPAA will never understand this.