Sure, you can now download music from the iTunes store without DRM but that doesn't mean you should just willy nilly start sharing that music with your friends. For one thing, it's illegal. For another, your account information is embedded into that m4a music file. Don't believe me? Try this yourself.
1. Launch Terminal. You'll need to be comfortable at the command line to perform this check.
2. Navigate to one of your iTunes plus downloads. If you have a US iTunes account, you can download the iTunes plus "Ooh La" single of the week.
3. Use the UNIX "strings" command to look at the text in your data and grep to search for your name. e.g.
strings 01\ Ooh\ La.m4a | grep name
Alternatively, open all the strings in TextEdit:
strings 01\ Ooh\ La.m4a | open -f.
Bottom line: DRM-free doesn't mean that Apple suddenly supports piracy.