I have currently put over 4,000 miles on a set of Gripsters and the tires appear as though they will last another 4,000+ miles. I ride a KLR650. The Gripsters are far superior to the factory Dunlop tires. The Gripsters literally grip the road whether wet or dry, and they do rather well off-road in gravel, sand, clay, dirt, and mud. I will purchase another set of Avon Gripsters when these need replacing. That is, if they are available at that time, whenever that may be.
I have used many pairs of these over 100K miles on various bikes including my Triumph Thruxton, W650, and even my R100RS. In my opinion there are better tires if you want to spend a bit more, such as the Michelin Pilot Active. These tires wear unevenly over the tread pattern when pushed hard, especially the rear. I suspect this may be from my riding style, leaning hard on the throttle while deep in corners. I have had two rear tires form cracks in the center grove, but not to the point where I replace them immediately. Traction is good, and they remain stable until you get near triple digits, or until the wear pattern becomes too uneven. I get between 3-5K miles out of a rear, 4-7k out of a front before they are ready to switch out. I continue to use them primarily because I think they are about the best bang for the buck out there, and I will not use "cheap" tires.
I have less than a month on the new Avon Cobra wheels so temper my enthusiasm. I had Dunlops and Metzelers before these and neither gave me the level of confidence I have in the corners like the Avons do. I am able to take them at a significantly quicker pace now than I remember on the others. No rain experience yet and can't comment on tread life for a few more years.