Originally Posted to the 318 TechJournal:
318 has open sourced our mergeSafBookmarks python script. This tool can read in a pair of property lists and merge them into a single resultant bookmarks file for Safari. This takes a lot of the work out of pushing bookmarks to existing users as part of your deployment. You can find it here:
http://mergebookmarks.sourceforge.net
Note: The script also looks at existing bookmarks and doesn’t merge in duplicates.