Sweet post Daggar
An open element type breather on the valve cover will allow unmetered air to enter the engine via the pcv. Normally the inlet to the valve cover comes from teh throttle body. This allows the air that does enter the intake via the pcv to be registered by the MAF. With an open element breather on the valve cover, the air that enters the intake manifold through the pcv is basically a vac leak.
I have heard some say they do this without consequence, but this setup could cause surging/hunting idle, and lower fuel economy (same as any other vac leak).
Just and fyi,
jason