If you want to clone frequently, cough up the $28 for SuperDuper. It has a 'smart update' feature that only copies changed files after the initial clone, so subsequent clone jobs finish much more quickly. You can also schedule jobs with the paid version.
The curent version of Carbon Copy Cloner has this feature, too.
rsync does that, too. Plus it's open source and has a nice, easy-to-automate command line interface. You can even use it to securely backup to another machine over the network (via ssh).
