I have several pairs of Earth (Vegan) shoes, including the cross trainers. I haven't really used them for cardio, just walking and weight work. The slight tilt of the shoe makes takes a bit of getting used to, and I didn't want to risk an 'oopsy' while stepping or doing other cardio.
I don't think Earth shoes particularly help with arch or heel problems. What they are supposed to do is allign your body the way it would be while standing on sand on a beach or in a yoga pose. In fact, they might not be that good if you have heel pain, because there seems to be a bit more force on the heel than with regular shoes.
For arch problems, I would highly recommend Birkenstocks (though I don't think they make any kind of workout shoe). My chiropractor does a neuromuscular test to see if whatever shoes one is wearing put one in allignment, and while Earth shoes were 'okay, but not perfect,' both Birkies and Teva's tested 'perfect' for me (which means they are the only shoes I should wear without orthotics).