Originally Posted by PursuedAdventures

Manneca has a great point. It's all up to how much you personally value your miles. For me, I would never use my miles to purchase goods from the UA shop. I just booked a 27,000 miles trip from Los Angeles to Shanghai, by way of Europe on both the outbound and return, in First and Business class for 140,000 miles and $144 in taxes and fees. That trip easily would cost over $10,000. I'm not good at math but I'm pretty sure that's at least 37 cents per mile (10,000 divided by 27,000 = .3703).