You can also purchase additional storage. Click the Buy Additional Storage link at the top of the page and you'll find that you can purchase 20, 50, 100, 200, 500, and 1000 GB plans for $1 per gigabyte a year. (That means $20 a year for the 20GB plan and $1,000 a year for the 1000GB plan.)

You also get a free sort of storage when you purchase music from the Amazon MP3 store. When purchasing digital music, you have the option to store it on your Cloud Drive. These purchases don't count against your storage limit.

Note that this storage can be used for more than music. At the top of your Cloud Player window, you'll find a Cloud Drive link below the Upload to Your Cloud Drive button. Click this link, and you'll see four entries--Documents, Music, Pictures, and Videos. Select one of these entries, and you'll find the option to upload content to your Cloud Drive using the standard Mac navigation window.