I'm surprised that you are shocked by it, there have been several threads on FT about taxes and an estimate of USD 1000 for a DONE4, so it should have been exactly what you expected. The UK tax taking effect in 2007 does add significantly, as pointed out by christep, but I think you only have one exit from the UK (otherwise it would have been higher). Avoiding LHR does save almost USD 200, but costs lots of mileage and routing. Most of the "taxes" are actually surcharges, both fuel (by the airline) and facility usage (by the airport). These are flat rate, not a percentage (so become a higher percentage the cheaper the ticket is). But 20% tax is nothing these days, I've had several tickets in the past year with 100% tax (some countries have high inspection fees). And of course the LCC tickets in europe for "1 euro" wind up costing 50 euros of "tax".

Now you know why there has been so much discussion about AA issued tickets (AA collects less fuel surcharge than the other OW airlines).