There is a term in music called "public performance fee." That is the money that artists make when their music is played for a live audience. Advocacy groups, like RIAA, believe that there are several types of "public performances" that aren't currently being bought. The most prominent of these is the preview on iTunes.
Now, if you have ever used the preview option, you know that you only get a 30 second sample, in fairly low quality, just so you can figure out if it is the song you are looking for. Have you ever used that preview to entertain an audience? How about to create a soundtrack for a film? Chances are, probably not. These groups are lobbying Congress to pass legislation to consider your personal use of a preview to find a song the same as playing the full song for an audience of hundreds.
If these laws are passed, there will be little to no affect on the populace, but I would imagine that Apple, and other digital distribution services, will no longer offer the preview option in their services.
Will the loss of preview prevent you from purchasing from the iTunes store? Or do you just download all of your music from BitTorrent anyway?