Like Kirstieuk says, no real change for passengers to the US - 2 pieces, but at 23kg max per piece (from September).
Two pieces at 23kg per piece is completely inline with the US airlines (certainly AA and UA - which I have both flown with recently...). Because we tend to take internal flights in the US, I have had to reduce our luggage weight accordingly for the past year or two anyway.
Edited Press Release
LONDON (Dow Jones)--British Airways said Thursday that it has always charged for excess baggage but is revising its charging policy, which comes into partial effect next Tuesday, to simplify existing policies.
Currently, more than 98% of customers travel within their free luggage allowance. The majority of these customers check in no more than one item of luggage per person. For these customers, there is no change.
This includes all travellers to the U.S., the Caribbean, Nigeria, Mexico and Brazil. Customers for these destinations will still be able to check in two pieces of luggage free of charge. The free 23kg allowance for economy-class customers to other destinations will be limited to a single item of luggage.
British Airways said it has no intention of discriminating against passengers who cannot comfortably carry a 23kg bag. Where it is clear that a passenger cannot manage one bag, we will let them check in an additional bag (or more) provided the total weight is within the 23 kg limit.
For the 2% of customers who wish to exceed their free allowances, the airline has decided to simplify the charges they pay to make them easier to understand.
At present charges vary according to weight, route and class of travel. The airline is replacing these with three simple rates for bags additional to the free allowance:
* GBP30 per extra bag on domestic flights, GBP60 per extra bag on European flights and GBP120 per extra bag on longhaul flights. Customers will get a 30% discount on these rates if they pre-pay online. The changes will not come into full effect until September.