Drupal 7 has a module, Read Only Mode, which allows your site to be viewed while in maintenance mode. No changes can take place to the database, but viewers can still see your site. This allows you to make your maintenance mode changes while not inconveniencing users who simply want to view your site.
Does this work with Civicrm as well? ie, does it prevent civicrm from changing its database while in maintenance mode?
We'd be very happy to be able to use Read Only Mode during Civicrm upgrades, which can take a while. Thanks for any thoughts!