According to Apple’s website, Apple’s iTunes Match is now available to the public. Originally scheduled for last month, Apple’s cloud music service takes the music you own and compares it to Apple’s catalog.
If you own it, you can then stream any of that music to your devices registered with that iCloud ID. If you’ve procured music from other than Apple’s iTunes (legally or by other means) and you pay a $24.99 annual fee, you can also stream that music as well, assuming that it is in Apple’s catalog. Regardless of the quality of the music file on your local storage, if it matches, what plays back does so via streaming with 256-Kbps AAC DRM-free quality. If you’ve got music in your collection that iTunes can’t match, you can upload it if you take advantage of the service.
Some see this as a one time amnesty and they are probably correct.
In order to take advantage of iTunes Match you’ll need to update iTunes to 10.5.1. So far that isn’t showing up as being available here yet.