Here's another example of using preserveViewport (although I am letting Google set the zoom)
http://www.mappingsupport.com/forum_post/preserveViewport_kml_35.html -- You received this message because you are subscribed to the Google Groups "Google Maps JavaScript API v3" group. To post to this group, send email to google-maps-js-api...@googlegroups.com. To unsubscribe from this group, send email to google-maps-js-api-v3+unsubscr...@googlegroups.com. For more options, visit this group at http://groups.google.com/group/google-maps-js-api-v3?hl=en.