Valid through January 31, 2014:
As reported by Miles4More, American Express is once again offering a great transfer bonus from their US Membership Rewards program to British Airways. Through January 31, Amex is offering a 40% transfer bonus to British Airways Avios!
Normally I’d recommend keeping Membership Rewards in your account until you have a concrete plan for how to use them, but in this case there’s a strong argument to be made to do the transfer prospectively since British Airways points are extremely valuable for certain redemptions. See “Big Wins”.
Of course, you should investigate beforehand to make sure that you’ll be able to use those Avios points effectively. With this transfer bonus, it would be reasonable to look not just at the usual British Airways sweet spots (e.g. short, direct economy flights), but also to other options. For example, one way in business class on Cathay Pacific from Chicago to Hong Kong would cost 70,000 Avios. That would require only 50,000 Membership Rewards points: