The trick is to move the folder with all your Safari preferences into your Dropbox. This folder contains your Bookmarks, History, and other information – including security sensitive information such as browser history and form auto-fill data (though the latter is apparently encrypted). I assume that you want to sync all of this stuff:

  1. Move the folder ~/Library/Safari into your Dropbox
  2. Make a symbolic link from the old location to the new Dropbox location. You can either use the terminal and type
 ln -s ~/Dropbox/Safari/ ~/Library/Safari

or use one of the tricks discussed in the other articles in the wiki to achieve the same thing.

All changes made to your bookmarks in one browser should now sync to all your other machines.