There is also a paradox created by airline pricing models. Let's say you need to travel transatlantic this week or next. It will be too late to qualify for discounted business class fares, but award availability may be excellent because many carriers allocate more inventory immediately prior to departure. In this circumstance it may even be rational to purchase the full amount of miles required for a redemption ($2,000 +) rather than pay the lowest available business class fare. Membership Rewards' 500,000 point limit and instant transfers make this feasible.
dennis
Been there, done that, it is a FANTASTIC option to have.