As stated above, the PCV system is great for oiling up the intake manifold. When you get time, remove your throttle body and look into the intake with a flash light. You will see the inside has a film of oil all over it. I can post up a picture of my heads (lq4 with 159,*** miles before it died from lifter failure) that I took off that after cleaning in the parts washer, is still covered in build up. This PCV system is used to pass emissions and reduce carbon output.
This thin film of crap from the PCV system leads to what is called coking up of the intake runners on the intake and heads. With the new direct injection motors, this will be much worse as the there is no fuel washing the runner down as it goes into the cylinder.
The build up of oil and crap via the PCV system leads to restrictions and lack of power. I swapped to the LS6 valley cover which is orifice based, doing away with the driver's side valve cover port. Also my motor is naturally aspirated as I don't have boost.