The first Porcupine I saw was on a CO elk hunt and I almost stepped on it.  The thing just stood its ground and watched us circle him.  I also ran over one with our minivan a couple years ago.  I tried my best to miss him and would have had he not decided to run back the way he came.  I dead centered him with the front and back wheels and couldn't have been more accurate had I tried to.  I don't see them very often and they seem so rare that it made me sick.  I've heard that they can be a real problem in some areas.