What PsyncX is for
PsyncX is a backup utility that allows you to backup only the files that differ between your backup drive and your normal drive. You can use it to synchronize all your files between different drives easily. If you use the full drive backup you will have a bootable copy of your main hard drive. You can also choose to just backup parts of your hard drive to another hard drive.
How PsyncX works
PsyncX is a GUI wrapper (this means that it is easier for non-techie folks to use) for the psync command-line utility. You can use it on any Mac OS X computer.