I think the rumors all describe a single device, This is the oversized that I'm calling the media pad, but could also be seen to be a small tablet or even a netbook without a physical keyboard, just one that appears on-screen.
Some have started calling this a tablet, which is true enough, but makes me think of Microsoft's not-very-successful tablet effort. Apple, I think, could do better.
Suppose Apple were to do a tablet PC right. Call it the MacPad: A MacBook or MacBook Pro with both a keyboard and a screen suitable for writing or drawing. It would be a major departure from current Apple touchscreens, which are not intended for use with a stylus--useful for drawing or notetaking.
This dual mode touchscreen could prove very interesting, allowing more handwriting recognition that could potentially drive Mac sales and improve applications. Artists and photographers, many of whom already use third-party graphics tablets, would presumably flock to the new tablet MacBooks.
Handwriting could become a much more standard part of Mac apps. Microsoft has tried this, but Windows tablet PC hardware remains far from common. Apple might better popularize a computer that is optimized for handwriting than Microsoft's partners have been able to.