Not yet, but after seeing this last week...I'd really like to get one:
The One and Only Tablet Mac
Designed in California by Axiotron?s team of German and American engineers, the ModBook? is at its core an after-market hardware modification to standard off-the-shelf AppleŽ MacBook? systems, converting them into high-end slate-style tablet computers. With its condensed form factor and integrated pen-based user experience the Axiotron ModBook is the ultimate companion for applications and situations where a keyboard only gets in the way.
http://www.axiotron.com/index.php?id=modbook