You mean the ZX-14, as it's called this side of the pond? Yes, I have.
I picked up my '06 FJR at the same time and from the same dealer as a friend of mine got his ZX14. We've both put about 1200 miles on our bikes and I had the opportunity to trade with him because my machine seems to have a driveline vibration that kicks in at about 180kph and runs all the way up to 240 or so (didn't ride it any faster) and he owned an '03 FJR that he got rid of after Yamaha fixed his ticking, so I wanted his input.. I took it for about 100 miles on a major highway (unfortunately - would have preferred a 2 lane twisty road).
I am not a sportbike fan. I don't like the very aggressive riding position, but I took the machine up to about 230 kph and, in spite of, or perhaps because there is zero wind protection it wasn't all that bad - the 'crane your head back' issues were self-regulated by all the wind.
Power-wise it was 'nice'. There was so much hype, that I was not overwhelmed by the FJR and, while the ZX14 was faster, it didn't blow me away either. It really was quite tame, when compared to my expectations - and I do tend to twist the throttle pretty hard.
However it was fast and it was smooth. The transmission is very precise and the power delivery was good, with a definite kick above about 5K. It is low, so it seems very stable. I was on a 4 lane divided highway, so I couldn't put it through it's paces handling-wise, but from the lane-to-lane and side-to-side shifting I was able to do, it does seem to handle very well. It has a six speed tranny - I'd have liked to see a 6th gear on the FJR, but that's about the only significant plus in my book right now.
Would I buy a ZG1400 or whatever Kawasaki might call a touring version of this machine? I don't know. Will Kawasaki build a GTR1400? I don't know and Kawasaki isn't saying whether they will or what it might be if they do. Anyone who 'knows' is a liar, unless of course they work for Kawasaki Japan, since they no longer build bikes in Lincoln NB.
No matter what they build as a touring machine (if they build one), about the only really major items it will have in common with the ZX14 will be the fact that it has 2 wheels and displaces 1400 ccs - they will retune it. They will change the ergos. So the bikes will be fraternal twins and therefore not directly comparable.
We'll all have to wait and see what (if anything) Kawasaki comes up with to replace the Concours.