EDIT: Austinrunner provided great information that I hadn't found before on how award tickets involved YQ can trigger all sorts of taxes that are never charged on YQ-free award tickets (e.g. ones purely on AA metal).

Hopefully this can be an example for everyone else on how YQ drives costs up beyond just the YQ

I just booked an award:

ORD - DFW - MAD: AA metal
MAD - ORD: IB metal
ORD - SJU: AA metal - free, thanks for teaching me about free oneways FT

First of all, a number of the taxes went up as of 1/1/13 so the amount quoted when I put the reservation on hold also went up once finally ticketed.

Second, below is an example of what taxes would be without YQ triggering paid ticket taxes.

ORD - DFW - MAD
1. Sep 11th Fee - $5.00
TOTAL: $5.00

MAD - ORD - using ITA to calculate taxes
1. USDA Aphis Fee (XA) - $5
2. US Immigration Fee (XY) - $7
3. US Customs Fee (YC) - $5.50
4. Spanish Airport Services Charge (JD) - $30.10 (up from 21 Euros = $27.72 the day before)
5. Spanish Security Tax (QV) - $5.40
6. IB Fuel Surcharge - $39.60 (30 Euros is the max IB YQ surcharge on AA Award tickets for a segment)

ORD - SJU
1. Sep 11th Fee - $2.50
TOTAL: $2.50

I add this together and I get $119.32. However, when I look at the ticketed price, AA seems to be including:

1. US Departure Tax of $17.20 for both ORD - DFW - MAD and for ORD - SJU
2. US Facilities Charges of $9 for ORD - DFW - MAD and $4.50 for ORD - SJU
3. US International Arrivals Tax of $17.22

Lesson learned - even $1 of YQ ($39.60 in this case) creates $65.12 more in taxes.

Were I able to do this trip entirely on AA metal, the total cost would be $60.30 ($5 for ORD - DFW - MAD + $52.80 for MAD - DFW - ORD + $2.50 for ORD - SJU) vs. $163.20 for just flying one segment on IB.