Advocacy groups representing songwriters, composers, and music publishers are hoping to carve a bigger piece of the download pie for themselves by re-classifying some electronic uses for their work as "public performances." They even advocate being paid when you click the "preview" button in iTunes.
A "public performance fee" is usually paid when a song is performed to a live audience, included in a movie you watch at a theater, or broadcast in some way. So songwriters and publishers are not getting performance fees for music that plays in the background of movies and TV shows, music streamed via internet radio and the 30-second song previews that iTunes and other music sites feature. They don't like this at all. It's not that they don't get paid at all, though. They're paid "sync rights" and "mechanical rights." But these fees aren't enough.
The songwriters and publishers are lobbying Congress to pass legislation that says downloads involve performance rights, in spite of the fact that they don't... at least in my opinion. But whether or not I'm right, it seems that the laws covering rights for music need a serious overhaul in the digital age.
As far as what it means to you, the consumer, probably very little. I guess if the law does change, iTunes might stop offering previews of songs, but I don't think it's likely to happen. Anyway, I'll bet you just steal music from Bit-Torrent anyway, don't you? Criminal!