All is well with the Drag and Drop chapter. The approach and methods used in the book are all valid and supported at this time.
I found this additional information in the Apple Documentation:
[b]The NSDraggingSource protocol declares methods that are implemented by the source object in a dragging session.
In Mac OS X v10.7 and later NSDraggingSource is now a formal protocol and has an updated interface. The Mac OS X v10.6 behavior has been retained, but will be dropped in a future version of the operating system. The methods that are to be deprecated are marked as such.[/b]
I do not know if these or any related changes provide any new functionality or dramatically change the look and feel of Drag and Drop from a user perspective.