When I press to backup the registry the dialogue box suggests that it will take some time but returns in about 5 seconds.  Is it really backing up?
Same for compacting the registry.

In the "Open with" list it would be nice if the associated program list could be sorted by cliicking on the column heading (standard windows behaviour) instead of having to find all references to a particular program.

   You should get an error if something went wrong during Backup.  Registry Backup on my computer takes about 50 seconds.  If you computer is faster than mine and/or you have less in the registry, it could finish in about 5 seconds.  I agree that that is fast but without any errors there is no reason to believe that it didn't work.
   You could go to the Backup (located in Windows\System32\RegVac) and compare the files in the backup with their original files (the location of the original files is listed in the user.ini file).  The backup file and original file should be close to the same sizes.  Some will not be exactly the same.

   I have added that ability in RegVac's OpenWith Editor.