Blank slate invitations (a term taken from the book Designing Web Interfaces) are inline invitations/instructions on how to interact with the UI - primarily aimed at novice users. That is, e.g., when no data are yet added, the data-presenting controls of the UI accommodate these instructional overlays. An example could be the text "drag items here" on a blank list of items.
What are your practical experiences with blank slate invitations? Do you have any good examples on how to/not to do it. What are best practices?