According to the two TechNet articles below, a user with the ‘take ownership’ permission on a file or folder should be able to assign ownership to a group of which they’re a member. Unfortunately, it doesn’t seem to work that way. An error is thrown indicating that the user should have ‘restore files and directories’ permission in order to assign ownership to a group.
Thanks! to FK for raising the issue (which contradicts information in the NetVision paper on Windows Access Rights) It’s a fairly obscure find, but worth understanding.