For a 30-cent premium, each track will be de-DRMified and encoded in 256Kbps AAC format, which should sound notably better than the 128Kbps AAC format standard on iTunes today. Users who already own DRM-protected EMI tracks will be able to upgrade to premium, non-DRM tracks for 30 cents a pop, too. And for those who don't want to pay extra, Apple will continue to offer EMI's catalog in the traditional 99-cent, 128Kbps, DRM-protected format.
EMI is one of the world's "big four" recording labels, and its catalog includes songs from artists like Radiohead, Queen, Iron Maiden, Gorillaz, Daft Punk, and of course The Beatles. Today's announcement seems likely to push the other three major labels—Warner, Sony BMG, and Universal—to eventually offer DRM-free music, as well. Apple CEO Steve Jobs certainly appears to think so: in Apple's press release, he states, "We expect to offer more than half of the songs on iTunes in DRM-free versions by the end of this year."
Update: According to an EMI executive quoted by the Associated Press, EMI's music offering on iTunes still won't include songs by The Beatles. Thanks to TR reader Snake for the heads-up.