"Super" Tweeters for new digital formats?

Has anyone heard some of the speakers being designed to accomodate the SACD extended frequencies (i.e. Tannoy, Sony, etc)
How do they sound? Does it make a difference?
I read some related info on the B&W website.
Sounds interesting! Hope us humans can hear it, and not just the dog!!
Did you see "Examining the Tannoy Super Tweeter", Robert E. Greene in the latest April/May 2002 TAS? Seems like a subtle but positive benefit from super tweeters according to his write up.