KB05483-New features of BlackBerry Browser in BlackBerry Device Software version 4.2
Auto Synchronize
This feature allows BlackBerry smartphones to set up the BlackBerry Browser to automatically scan for updates to bookmarks and web feeds stored. When a bookmark or web feed is added or edited, it can be specify how often the BlackBerry Browser should check for updates to the web page in the Auto Synchronize field. When the BlackBerry Browser scans a web page that has been updated, the bookmark or web feed will appear in bold and italic.
It updates the bookmarks. It doesn't "pre-download" the pages.