^also, putting a filter on the pcv system is not really a good idea because it will create more pressure in the engine compared to an "open" venting system without a filter. This increased pressure can cause seals to blow out, and actually can cause you to lose a few hp. Many drag racers run a system that ties the pcv/valve cover vents into the exhaust and the exhaust creates a vacuum that "sucks" the crankcase pressure out. Alot of people never change their PCV valve, and if blocked it can cause excessive pressure and blown seals. It is good cheap insurance to replace the pcv valve every 50,000 miles or so, even if they say every 100,000, they are only a few bucks. Just my opinion, I try to change mine more often, or at least clean it.
Breathing in and out is good enough for me.