Very interesting article. I find the following quote from the article very interesting:
The airlines are happy to support such a scheme, since they contribute almost no funding to the redemption mechanism. It's virtually a "free burn" for them. Likewise, Milepoint.com contributes no funding to the redemption. The value, such as it is, is contributed by the retailer in the form a discounted price on his goods or services. Describing this as "turning miles into money" is at best an exaggeration.
When I was buying from Amazon I had a choice of using no miles and using a $15 coupon code for the purchase and I could also double dip and get an additional cash back. Or I could burn 750 miles at milepoint and get the same $15 off.