Thanks for the info Wino;
This is the first time I hear about this with the A320 and I flew 4 years on this aircraft.
Anyway, what follows is an extraction of our company's "Pilot Notes" about the 737-800 NG Introduction:
"Fuel tankering and wing icing:
Because the amount of fuel in the main (wing) tanks is less than on the B737 Classic, the chance of landing with full main tanks when tankering fuel is greater than on the classic.
The result is the possible appearance of icing on the upper wing, due to the condensation caused by the fuel cooled during the cruise part of the flight. Icing may occur even with an OAT above 20°C.
A take-off with any kind of contamination on the upper wing being prohibited and de-icing being unavailable in TFS and HER and other places, this situation may prove to be very disruptive to a smooth operation.
..."