Hi Rob,
I had a CBR600fx model before my Duke, I think thats the same model as the one your looking at.
I did have my fair share of problems with it, blown regulator which fried the dash, rusty centre stand after first time getting wet and gearing a little on the high side (as all bikes I feel), and quiet like a hairdryer.
The last problem (quiet like a hairdryer) caused me to sell it as a kid ran out in front of me not knowing I was coming!!! Certainly wont do that on the Duke
No real pboems although I've heard about the cam chain tensioner as all IL4's.
Andy