iTunes Plus has mainly been limited to EMI and some independents so far), and that most previously purchased songs are now upgradable for the same old price of $0.30 a song. We're still digging around on the iTunes Store trying to figure this out -- it's offering to upgrade our library, but the transaction won't go through yet -- and we'll obviously know more if it gets a keynote mention. Let us know if you have any luck picking up those non-EMI MP3s on your end.
Update: As you've you probably noticed in the liveblog, Apple just made this very much official, and announced that some 8 million songs from all the major labels will indeed be DRM free, with a full ten million planned by the end of the quarter. As if that wasn't enough, it's also announced a new pricing structure for tracks, including a new $0.69 tier and a $1.29 one, which music companies will apparently be able to use at their own discretion. And, to keep things really spicy, the company has also announced that music store downloads are now finally available over 3G, and at the same price and the same quality.