If you want to make an exact replica of your Macintosh HD, use SuperDuper!
I recently wanted to re-do my home iMac from scratch as i had been using it for two years without one and decided a fresh-start is what it needed.
I cloned my Macintosh HD using, SuperDuper! to an external harddrive i had lying around.
I then re-installed Mac OS X from the original discs that came with my iMac (10.4.6 i believe) making sure i used the ‘Erase and Install’ and not the ‘Archive and Install’ option.
Once all set-up, i re-connected the external harddrive, pulled off a few folders that i was after (iTunes Library, iPhoto Library, numerous widgets, Firefox & Thunderbird user-data folders etc.) and Voila! a new system, without the headache.
So did it work like how i wanted? Absolutely! My ‘Sims 2’ installation (with every Mac expansion pack available at the moment) has never been faster and i’ve definitely noticed speed gains in every area of the Finder, along with Firefox and Thunderbird.