i have had minor problems with my heating ventillation system when i set the heating to come out at the windscreen, half comes out by the footwell aswell. this has made me learn more about condensation a lot more.

some points to note:

a) air con will clear the misting up very quickly as the air con has a de-humidifyer,

b) if the air con has been on for more than 30seconds or so and then you turn the air con off you will start to get condensation build up again. the only way you can avoid this is either to:
1) make sure that you havent had the air con on for 30mins or so,
2) if you have had the air con on then keep it on, or turn off the air con and wait till all windows clear before you go drive more,
3) make sure that you use cleaning products that are specificcaly designed to be used on car windows. please note that some home window cleaners such as 'windowlene' will make condensation worse. (maybe the valeter used something like this)

I have noticed that after it has rained and you open the rear tailgate the water runs off the glass back towards the car and overspills into the boot area. Think this is because there is no gutter.

Anyway this water quite often causes condensation, but after a minute or so all is gone with the air con on.