Steve Jobs confirmed to the Wall Street Journal what Ars Technica reported earlier: iTunes Plus songs sold via the iTunes Store are now 99 cents, down from a typical $1.29. iTunes Plus songs are sold without digital rights management (DRM), which encrypts content for playback on specific devices in specific ways.
The impetus is likely the launch of the Amazon MP3 music store, which offers DRM-free music for 89 to 99 cents per track from both EMI, which Apple carries in DRM-free form, and Universal, which has declined to make such a deal with Apple (see "Amazon MP3 Takes on the iTunes Store," 2007-09-25). Both stores include DRM-free music from many independent labels as well. iTunes Plus songs are encoded as 256 Kbps AAC files; Amazon's music is all 256 Kbps MP3. iTunes has over 6 million songs; Amazon, over 2 million.
What's not clear yet is whether it will still cost money to convert iTunes songs with DRM to iTunes Plus songs if the cost is the same; whether you'll be refunded any previous upgrade fees for iTunes Plus (unlikely, in my view); and whether Apple will list iTunes songs with DRM alongside the same song without (also seemingly unlikely).