In my opinion, the best value for Membership Rewards points is the airline miles transfer program, and the best time to do a transfer is when they run a promotion such as this one. From now until May 31, 2012, earn a 50% bonus when you transfer points from Membership Rewards to British Airways. There is no need to register, and you can transfer as many times as you like before the promotion ends. The smallest increment you can transfer is 1,000 points.
The highest yields can be found on popular tourist routes that are typically short in distance but high in cost. For example, the San Francisco to Los Cabos route is quite popular, and Alaska Airlines can charge upwards of $500 or more for this three-hour flight. However, only 20,000 Avios points are needed to book a round-trip award ticket, while using other frequent flyer programs typically will run you 35,000 miles. Likewise, flying Los Angeles to Honolulu on American Airlines costs only 25,000 Avios points. Even shorter flights such as San Francisco to Los Angeles, New York to Toronto, Miami to Cancun, Lima to Cusco, all only cost 9,000 Avios points round-trip! Read my previous post to find out how to price out specific award itineraries on the British Airways website.
If you have a large stash of Membership Rewards points just waiting to be used, I would highly recommend converting at least some into Avios points before May 31, 2012. Although others may disagree, I would do the transfer even if you don't have any award travel planned. Typically, transfer bonuses don't get any better or simpler than this. Membership Rewards did run another promotion last year where you could effectively earn a 67% bonus on Delta Skymiles transfers, but it turned out to be a logistical nightmare, and people had to wait months before they actually received the bonus points in the form of a rebate certificate. Plus, I have not seen any transfer bonuses higher than 50% for Membership Rewards to British Airways.
I don't doubt that another 50% transfer bonus promotion will occur sometime in the future, but I say take advantage of the offer now, and make use of those Avios points for high-value redemptions before another devaluation comes!