The accuracy depends on the firearm. Full auto is only good for two things in my opinion. 1 Suppressive fire (i.e. making the enemy get there heads down), and 2 Point blank range/room clearing.
Some firearms are very accurate in full auto though, some of the WWI MGs on the tripods come to minds, as well as some other firearms like the MP-5s which just due to the caliber of the round tend to stay on target much more effectively (though the caliber limits them to point blank range anyways).