After typing a long entry into the Add New Page section, I clicked Preview, saw some minor formatting issues I wanted to correct, so naturally I clicked the Back button on my browser. Wham! All that typing is gone! Forward button to try to go back to the preview says 'Page expired'.
This is a no-brainer. Never have a 'feature' that destroys a user's work. This is why we have Recylce Bins, Outboxes, Undo, Shopping Carts, and all these other metaphors.
Either the back button should not destroy the text in the browser's memory (a la WardsWiki), or the text should be kept in a safety session object (a la HotMail).