Phil: the preview specifically stated that you would lose information if you then went to the actual 8.1 update.
Re: 8.1 preview.
"If your PC was running Windows 8 (before the preview install) you might be able to restore it back to Windows 8 by using PC refresh. Your personal files won't be affected, but apps that did not come with the PC will need to be reinstalled and apps that you installed while using the preview might not be available through the Windows 8 Store. To find out more about using PC refresh, see Restore, refresh, or reset your PC. "