Nothing like a customer service tale with a mostly happy ending: Nathan switched computers and lost everything he bought from iTunes (music, ringtones, movies) as a result.
So he wrote to Apple ([email protected]) and they agreed to let him re-download all the music he bought at no extra charge:
I understand the titles you purchased from the iTunes Store with account [redacted] were lost. I know how upsetting that can be. My name is Jesse and I would be more than happy to help you with this today.
Seeing that you have been a loyal customer since September, 2004, the iTunes Store would like to give you the opportunity to re-download (at no charge) all the titles you purchased on this account that are still available. This does not include any item that has been modified or removed from the store since you purchased it. Please note that you may download your purchases only once, so this is an exception. Also note that Apple does not offer protection for the loss of data from your hard disk, so I recommend that you back up your iTunes library as soon as possible…Full email from Apple at Consumerist.
Nathan was also able to re-download ringtones, but not movies though the rep did not provide an explanation for why not.