When Walmart ditched its Amazon Prime-style subscriptions and offered free two-day shipping for all orders over $35, it was a shot across the bow -- we might not compete directly, but we can still undercut you. Well, Amazon is responding in kind. Just a year after it hiked its free shipping minimum to $49, the online shopping giant has lowered that threshold back to $35. That won't deliver your goods any sooner (you still need Prime for that), but it could tip the balance if you're more interested in avoiding fees than getting your order in a hurry.