I've had some head shake on the FZ6 rip'in goat trails, ('think I need ta check mah steering head bearings?) but not a real "tank slapper" like this[ame="http://www.youtube.com/watch?v=sFcTi_qx6p8"]IOM_TT[/ame]
With head shake, you just get the bars violently flicking back 'n forth, usually brought on by a bump, but if you relax and don't fight it, it'll go away when the energy of said bump is gone.
With a real tank slapper, (As above) you have the motor exceeding the ability of a flimsy chassis, or other mechanical failure, and the whole bike wobbles outta control; nearly impossible to recover from.
The FZ6 is purdie stable and not in need of a steering damper.
Kawasakis from the '70s and that Honda 900 Fireblade were notorious for tank slappers; I believe this is a Honda 900 in the video.