Move WSUS server to a new server

1. Install WSUS on your new server, making sure to select the option to use the existing Windows Internal Database
2. During the Choose Upstream Server of the configuration wizard, be sure to selectSynchronise from another Windows Server Update Services Server
3. Ensure that the This is a replica of the upstream server check box is selected.  This ensures that existing approvals, settings, computers and groups are maintained
4. Complete this Wizard
5. Your new replica server will synchronise with your upstream server.  This is what we're talking about - no re-downloading many GB's worth of patches!  N.B.  Wait for this process to complete before carrying on with step 6.
6. Now change your Update Source and Proxy Server settings to Synchronise from Microsoft Update
7. Now for the magic bit.  Download and install the WSUS 3 API Samples and Tools on both your old and new WSUS servers
8. Open up a CMD Prompt and navigate to "C:\Program Files\Update Services 3.0 API Samples and Tools\WsusMigrate\WsusMigrationExport" folder on your old WSUS server
9. Run "wsusmigrationexport.exe WSUS_Settings.xml" to export the settings. This will backup your approvals and target groups to an XML file
10. Transfer the WSUS_Settings.xml created above to your new WSUS server
11. Again navigate to "C:\Program Files\Update Services 3.0 API Samples and Tools\WsusMigrate\WsusMigrationImport" folder (on the new WSUS  server). Run"wsusmigrationimport.exe WSUS_Settings.xml All None"
12. Review and compare settings on your two WSUS servers, ensuring that they match each other
13. Update the relevant GPO's to ensure clients are pointing to the new WSUS server

One last point, I've noticed that if you are not using GPO's to assign your computers to Computer Groups all your clients will get stuck into the Unassigned Computers group.  You'll have to manually sort them into the appropriate groups again.  Bummer, but you really should be using Computer Groups....