The topic has been getting some discussion in several threads (
here's one example) on the Apple forums.
Better put the hammer down, Dave, and get a Leopard-compatible version of SD out quickly before even more users foul up their backups and subsequently their boot drives when they clone it back.
You don't need a public relations mess on your hands caused by people using 2.1.4 with Leopard. Or at least, start hitting the forums and explain exactly what is incompatible. Your brief note on the home page that "SuperDuper! 2.1.4 is not yet fully Leopard compatible" (without specifics) isn't explicit enough to keep people from trying it anyway.