I was under the impression that wheel spacers were generally bad, because they change the loading on the wheel bearings and stub axle, unless your using the spacers to correct the position of the centerline of the wheel on the axle, instead of adjusting the wheel for purely cosmetic reasons. Eg. if you has a wheel that was correctly centered between the bearings on the axle, but spaced it out to be flush with the fender (purely for cosmetic looks), moving its center further to the end of the axle, you would increase the loading on the outer bearing and the forces acting on the stub axle. So potentially I guess you could snap axles. Which is why they are illegal for road use in Australia. Or at least thats my understanding of it. Whats the story in the US?