clipped from: blog.wired.com 
With the launch of iTunes Plus, Apple's become the first to sell DRM-free music from a major label. Not included in the press release is the fact that all such downloads are watermarked, containing the user's full name and email address.
It's quite clever, when you think about it. The only way it could ever be a privacy concern for the user is if they do something they shouldn't, such as share the file with others. If you think that DRM-free music is an excuse to start throwing it up by the gigabyte on Bittorrent, there could be public humiliation and, perhaps, a legal suprise or two in your future.
Moreover, iTunes itself could easily spot tracks in its own library that have been illegally shared by other users. Perhaps by getting on the DRM-free bandwagon, Apple's managed to make itself the copyright entrapment-meister general.