What's more of a concern with using liquid helium, after you've shelled out a few hundred bucks for a tank, is not leaving the top open. All the other gases will form a layer of frozen air on top of the helium, yes frozen oxygen, nitrogen, and the rest. Then you've got a problem. Eventually, that helium's gonna warm up and expand. If you don't do something soon, the thing's a huge bomb. Usually, what's done is that they try to break through the crust with a metal pole at first, but if its too thick, they have to drill through the side of the tank, which I can't image how'd they'd avoid not freezing themselves when the liquid helium comes out.
What's interesting about oxygen, is that its paramagnetic. It'll be attracted to magnetic fields.
What's interesting about hydrogen, I think its hydrogen, is that they believe there's a metallic form that comes after solidifying it. They're waiting for it to turn from clear, to shiny like a metal, though I'm not so sure about the progress of that.