by Morgan Estes on WordPress.org
Remove the admin bar from the preview of posts and pages, with optional reminder notification bar.

Plugin options in the Writing options page.
If you find yourself previewing a post, clicking the “edit” link at the top, previewing that post, and eventually realizing you have 3 or 4 tabs open with different versions of the same post? Then you’ve felt the pain of editing in WordPress.
But now there’s hope! Simply remove the entire admin bar from your post previews and remove the temptation to edit a preview! Still need a reminder that you’re on a preview and you need to go back and save your changes? No problem, we’ve thrown that feature in for free! Don’t like it? No worries, simply check a box and preview your posts in all their life-like glory!
These features are planned for future releases: