Many of the Microsoft watchers and customers I know have been expecting Microsoft to ship the first service pack (SP) for Windows 7 and Windows Server 2008 R2 before the end of 2010.
Typical Microsoft policy: Q. Can I upgrade from the beta builds to the final build of SP1? A. No. You will have to uninstall the Service Pack or do a clean install of Windows 7 or Windows Server 2008 R2. Who needs the hassle? (Just wait for the final release!)