We just got this email from AA regarding our trip in Sept - LAX to Budapest, via Heathrow and the return Prague to LAX via Heathrow. We will be hit with the Business class retro tax.

"Following the U.K. Government's decision to double the Air Passenger Duty paid by passengers traveling from the United Kingdom, American Airlines customers who have purchased tickets to travel on or after February 1, 2007, will be required to pay the increased tax before flying.

For long-haul flights to the United States, APD (GB tax) has increased to:

£40.00 for Economy Class travel (previously £20.00)
£80.00 for Business & First Class travel (previously £40.00)

Customers who purchased tickets prior to December 12, 2006, will need to pay the extra tax at the U.K. airport when checking in for their flight. Payment can be made by credit card or cash.

American greatly regrets the inconvenience that this retroactive tax will cause our customers."