iOS 6 is available for download now, but like with any major upgrade, there were headaches that came along with it. The new OS has some teething troubles, notably a Wifi login bug that Apple has quickly and mysteriously resolved. Now other users are seeing other problems like accessing music on their iPhones.
The OS is heavy, and at 2.5 GB, you'll want to do this over a Wi-Fi network if possible. Apple servers managed to hold up pretty well but there are are some lag times among others, some saw the download happen from a few minutes all the way to five hours.
The Wifi bug, as many users have spotted brings users to a log in page that directs them to a non working URL at Apple.com when they attempt to log into a Wifi network which their devices had previously recognized and stored passwords for. The company acknowledged that it existed but shouldn't be a problem any more. The Wifi bug vanished almost as quickly as it was discovered.
For some users and this Apple support forum included — their music libraries had suddenly vanished. The tracks were unavailable.