I'm going to agree with everybody else here. It accelerates wear on certain components, but people wouldnt (safely) autocross old cars with 200k miles on them if it was hell on all the components. If a rusted out 86 VW can still get around the course safely, I think the Focus will be just fine for as long as I care to drive it.
2004 SVT Focus
Custom front-bumper-mount bug guts; precision sprayed brake dust on OEM rims; 15% Pine Tree pollen over the clear coat.
No more SVT autocross, I drive the thing in the avatar.