IO Karkand I see quite afew people who are blatantly hacking, but its not my server I can't proove anything so I just leave the server.
Outside IO(Karkand mainly) I don't think I've seen anything I would say deffo was a hack, I've seen some top players hammer a team but thats not a hack, I know alot of people go crying Hacker if your any good so I can understand some of the better players getting frustrated with it all.
I will only call hack against something I know 100% is dodgie eg, some chump called Liverpoolfc*** or something similar yesterday was blurring the SVD full pelt, no pause to re-aim(not even a split second) or even to move the cross hair and dropping 2/3 guys at a time. Everytime you tried to sneak round to cap a flag you'd emerge from a corner to have him standing crosshair on your head bosh!!.
I have seen some sh*t hot SVD user's, drop 4-5 guys perfeclty legit, but there is a pause in fire, no matter how short, no-one can go from head to head at max SVD rate of fire, every time without fail.
Even then I didn't start calling him a hacker, they love that it make them feel loved, I just asked him if he actually enjoyed playing like that, and laughed at the poor gimp, alot.
In away IO Karkand has done a favour for us, people go there to cheat, keeps most/all out the other game's, I know it's fun to play if every so often until you find one of these jack off's but they are getting more common.