There has been a bit of a controversy surrounding the DRM-free songs, as some sites have reported such tracks have embedded within them the full name and account information, including e-mail address, of who bought them. Although, this should only be a privacy concern to those users sharing files over p2p networks. Furthermore, iTWire makes some interesting arguments in a recent article saying this is a non-issue since DRM protected songs have always carried this information:
The difference is that it didn't matter with FairPlay protected tracks, as there was no point in spreading copies around. If anyone was planning to distribute iTunes Plus songs (and that would really encourage other labels to catch the DRM-free wave, wouldn't it?), this embedded data would act as a disincentive unless they found a way to remove it first.
And as for references to Apple acting "secretly" or "covertly" - get real! The information is stored in plain text.
Removing the embedded information from the tracks is probably not technically difficult; it is just a matter of time before someone finds a workaround, although I do think Apple is entitled to some kind of piracy prevention measures.