From now through January 31, 2012, receive a 30% bonus when transferring your American Express Membership Rewards points into British Airways Avios points. There is a minimum transfer requirement of 1,000 MR points. So for each increment of 1,000 MR points you transfer, you will receive 1,300 Avios points in your Executive Club account.
It seems a bit strange that American Express would be offering a mediocre bonus like this since they have previously run 40% and even 50% bonuses for British Airways points transfers. Even more so when you take into account the huge devaluation that BA just announced on November 16th. I certainly hope that AMEX will up their bonus offers in the near future. They certainly need to after Continental ceased to be a transfer partner as of September 30, 2011, and Air Canada's Aeroplan started adding fuel surcharges to certain partner awards. Membership Rewards points have become severely devalued as of late, so I would say that the only time you should really make any transfer is when they are running large bonus offers.
As for this offer, unless you have an immediate need to book a BA award flight, I would say hold off until a better promotion comes up in the future. Still, a mediocre promotion is better than none at all.