Apple has released iTunes 10.5.1 which officially launches iTunes Match.
Tunes Match was supposed to launch at the end of October but Apple has likely encountered some bugs that resulted in pushing back the release date. There has been an inactive toggle in iOS 5 since shortly after its launch.
iTunes Match allows customers to pay $25 a year to have their music libraries matched with the content available on iTunes at 256 kbps bit rate quality. For songs that aren’t available on iTunes or unrecognizable by the service, the user can upload the content manually. The songs will then be available on all Apple platforms (OS X, iOS, Apple TV) and iTunes as an option to download the content straight to that device to listen to.
Get iTunes 10.5.1 here or through Software Update.