Played a lot of TF2 now. Apart from the terrain exploits the only hacking I have seen is the sniper aimbot and thats so damn obvious. Its a bot people pay for, why the heck you would want to pay for an aimbot I don't know.
Apparently valve did manage to ban it in this last patch but the bot code was changed and back in action the next day.
i hate snipers in tf2 altogether, i think they need to do away with the machine gun and give them a pistol, they are overly powerful and just annoy me something serious