not true its front wheel drive and is only 4 wheel drive when traction is lost at the front 
100% correct.
More like 10% correct. It works on a constant 90/10 distribution and sends torque to the rear based on rotational differences front->rear. It doesn't have to be 'slip'
No it dont. You been reading too much crap from the fantasists at Haldex Traction.
For the nity-grity detail, for all standard Haldex controlers (and not aftermarket ones like a Gen2), the Haldex clutch is operated with a base setting of 5% clamping force (this is to keep the oil warm, as cold oil will shear the friction linings off the clutch plates). Therefore, the default torque distribution, front to rear is 97.5% front to 2.5% rear. The rears are NOT pre-emptively engaged - the rear axle is only sent more drive AFTER the electronics controlling the clutch has sensed that the front wheels are rotating faster than the rears - ie wheelspin. However, this is not a "finite" measurement, because the Haldex controller needs to allow for different axle speeds when cornering with equal grip - which is why permanent 4wd vehicles need a centre differential, and which the Haldex is not!
There is only ONE car in the VAG mainstream range which uses Haldex in a pre-emptive mode, and that is the Audi R8. The Veyron also uses pre-emptive engagement, but that is because both axles have a Haldex, and the leviathon wouldn't get off the line otherwise.
