...and I can only agree with most of what is already said. As I told Asbjorn myself - this experience (cost) is just the right amount to induce the proper amount of respect for this "drifting" - different location, higher speeds and it could have ended MUCH worse!
Weight distribution, soft suspension and open diff (Z4) is a dangerous cocktail to balance sideways. My own car is probably easier but I also find it rater unpredictable with the open diff.