Lorenzo Puleo has announced an update to his synchronization utility called Folder Synchronization. Folder Synchronization will watch two folder that you name and make sure that they mirror each other. Rather than deleting and replacing entire folder, Folder Synchronization will instead append new files to old directories in the same manner as Unix. The new version adds several new features. According to Mr. Puleo:
What's new in the 1.4 version
In the "Info" area there is a new check-box: "Exact BackUp". If checked (only together with "One direction only"), FS will delete, from the Bottom Folder, all the Files and all the Folders that no longer exist in the Top Folder. This way, the Bottom Folder will be an exact copy of the Top Folder, as the Finder has replaced the entire content of the Bottom Folder.
FS, which operates differently from the Finder, will copy only the Files and the Folders which really need to be copied, deleting in the Bottom Folder the Files and the Folders that no longer exist in the Top Folder, and therefore will take less time than manually doing the same thing in the Finder. Moreover, Filters can work together with this option. e.g. If you define a filter, FS will copy (or skip) and will delete (or skip) only those Files which match that filter.
Many customers asked this option, but use this option with care. THERE IS NO WAY TO UNDO THIS PROCESS!