I've had mine for around 6 months now and its been a fantastic commuter bike. Averages 65mpg in real world riding, 30/40/50mph areas and dual carriageway blasts too, i generally don't rev it more than 4/5k unless out on the open road.
Grumbly engine below 3k, has a definite powerband at 6k and max power is at 9.5k so pointless revving it any higher.
I've owned a '95 fireblade for 5 years, then a cg125! for 2 years, and now this gpz. It lives outside in all weathers and finish has hardly changed from an already good condition when i bought it(had been garaged out of the weather). Chain has not needed adjustment in last 1000 miles, but carb balancing is critical if you want as smooth an idle as poss. Very dependable, solid, heavy, and well behaved bike, but doesn't like idling on choke in the mornings for too long-seems to begin to flood itself no matter what position you move the lever, but as soon as ur on the move it just about idles ok from then on, even if it is freezing temperature outside, its yet to stall on me.
My milage is now 28,400miles, i've done about 1000 of those.
I genuinely get 65mpg regulary, which for a 60bhp bike is quite good!
My only bad points i should mention are the weak front brake-i've bled mine, fitted new piston seals and new genuine pads and they're still shockingly poor, single disc, 2 pot calliper is not enough on a 185kg bike.
Next up is the handling, around town its fine but once a more enthusiastic ride is underway you'll soon notice the rear feeling 'soggy' in corners, maybe partly down to shock condition but maybe down to the basic suspension design.
And lastly, the overtaking of cars. Generally you sit in the 3-4k band while riding which is a comfortable range allowing you to speed up or slow down easily in sync with other road users, but if you wish to overtake, you need to get the revs up to around 6k which means dropping 2 gears every time you want to scoot past the car infront.It gets very tiring doing this every time you want to overtake. This zipping past a car then highlights the poor brakes as you then have to slow for a second in order to not rear end the car you pull in behind! So the experience soon puts a dampener of this style of riding. I was used to a 'blade which you could open the throttle and have a surge of power in any gear, so perhaps that makes this feel like a bigger deal than it is, but i thought i'd mention it anyway.
Overall, a very recommended bike for commuting, 65mpg, reliable, solid feel and good resistance to corroding if kept outside in the bad weather.
Bridgestone bt-45 tyres are what i have fitted since buying mine(it did have avon roadrunners on)and they seem to be the tyre of choice for these bikes. They're £145 from black circles.co.uk per pair.
I really like my bike, it does exactly what it should do, just gets a bit out of its depth should you want to make rapid progress, but generally its a pleasure to ride in 90% of cases.