Your Apple ID can only be associated with 10 devices, 5 of which can be computers. Once a device is associated with an ID, it cannot be associated with a different ID for 90 days. Once this limit is reached, you can't use features like redownloading past purchases from this ID with a new device, which is what happens at the end of the iCloud restore process. You can still sync your purchased media to your device using iTunes.
This article explains this policy, as well as how to find out which devices are already associated with the ID: http://support.apple.com/kb/HT4627.