From the editing of any content in the website interface, you have access to the "preview" button. If you click on the preview button it shows you the preview, but there is no information indicating that its a preview. In the admin interface the preview is normally shown in an iframe, so its not that confusing.

When looking at the preview, its very natural to click "edit" in the ez toolbar to get back to editing. That gives you a "this is already being edited" warning.

I suggest either disabling the toolbar during preview (version-view) or use an iframe, so its easier to see that its a preview. Maybe a big "preview" heading on the top with a "back to edit button", and the preview underneath.