I'm contemplating upgrading from Windows 8 to the new Windows 8.1 Preview, but I've been unable to find whether it will be technically possible to upgrade from the preview to the full release. It apparently is with Windows RT, but I've found nothing about Windows 8 Pro.
Accordingb to Microsoft it is possible but it will wipe all installed desktop software and likely require reinstalling modern apps.
8.0 RTM -> 8.1 RTM : No loss 8.1 Preview -> 8.1 RTM: supported but loss.
incidentally explains all things in this regard.
I've found my own answer, from Paul Thurrott:
those who do install the Preview will lose any installed desktop applications or Metro-style apps when they later upgrade to the final release, which should be completed in August.
So, it appears that upgrading to the final release will be supported but it will wipe installed applications.
(I still can't find this information in the Microsoft FAQ at http://windows.microsoft.com/en-us/windows-8/preview-faq, although I'm assured it's there - so hopefully this question may help somebody else.)