I think if you really break traction suddenly with a lot of power and get the wheels spinning before the system has time to cut in then it doesn't intervene thereafter unless you back off. I've noticed this in snow. You can happily get the wheels spinning if you're clumsy with the throttle and the ASR doesn't try and stop it. However, if you are a bit more subtle the ASR does seem to kick in at the point of slip and take control. I'd have thought this should be more difficult to do on normal roads though unless particularly damp and greasy ... or maybe my ASR doesn't work properly either.