how about a db (especially if you make an app out of it), that stores portals (text is small in size), and lists moved/new/changed portals on the next refresh? You could make it answer questions like "which portals are new , moved deleted in my hometown since (date)"
Maybe you could make a firefox and opera compatible ,js out of it or a complete addon.
http://gallery.extensionfactory.com/labs/conversion/ can't handle queries, doesn't show the map for get bounds and gets stuck at querying.