Nothing yet, but then you wouldn't expect anything to go wrong yet would you?? Hopefully.
The only complaint I would have would be with Kawasaki's insistence on getting the first service done by a dealer to validate the warranty, & then the dealer charging stupid money to what effectively amounts to changing the oil & stamping the log book. Not usually a problem if you take the bike back to the place you bought it from through.
Since this is my first bike, & I haven't done any great mileage, I can't really be that objective, but out of the several bikes in the class bracket I definitely feel I've made the best choice.
Every time I'm out on it though, it never fails to put a smile on my face. And it easily is the better looking bike over say the Fazer & the Hornet 600's.
Performance, handling, etc for the bike are all way above my capabilities as a rider at the minute. Which will hopefully mean that I will be happy with it for several years to come.
The only small little niggle I've noticed so far is that the bars can be a bit vibby at times, oh & the air deflector which is supposed to create 'an air dam around the rider' really doesn't work at about 120mph.
It gets uncomfortable at about 2 hours.
Oh, & the girlfriend refused to get on the back, even after I offered to get her some leathers. Which was more for me I'll admit.
I have a Z750. Put on a Corbin seat which is much more comfortable, worth the money.
The Z750 was probably not a good choice for a beginner. You should learn to ride before you even think of taking pillions. Also if you find a Z750 uncomfortable after 2 hours, your riding position is probably not quite right. The seating position of a pillion on a semi-sports bike is also crucial for safety and comfort. If he/she is holding on just with the hands, it could cause you to become unsettled.