Ecto - it depends on what you mean by open. I never have too much need for a wide open hihat sound, so I usually just keep the cymbals maybe a quarter or a half-inch apart (when my foot is all the way off the pedal). That way you get that clangy sound of the two cymbals hitting one another, which is the way 99% of metal songs are played. That way your left foot is free for the second bass drum pedal...
So anyway the cymbals are pretty much always together, you just close them down a little more or a little less depending on what sound you are looking for.