Some negative camber is certainly a good thing for performance driving, but you don't want too much! Even lowering the rear end 2-3 inches can result in excessive camber.
The main problem with the Mk2's rear suspension is the way the camber changes as the wheels move up and down. So while you may have an acceptable amount of camber while the car is stationary (say, 3 degrees), you might end up with 5 degrees as soon as the back end is loaded up (eg under acceleration). That's definitely too much camber!
This is the reason Mk2's are difficult to launch well - as soon as you step on the loud pedal, the back wheels splay out and the tyres aren't contacting the road properly - say goodbye to traction and hello to wheelspin!
There are several ways to get the camber back to factory specs after lowering the suspension. Some are more effective than others, but none of them are particularly easy since there is no built-in camber adjustment for the rear wheels.
The quickest way is to remove the large rubber bushes which separate the rear subframe from the floorpan - this raises the subframe about 10mm and subsequently pulls the camber in a degree or two. My plan is to take this a step further and machine 5-10mm of metal off the subframe to raise it even further - this should allow me to lower the car at least 2-3 inches while retaining close to factory camber specs.
