I once went on a job interview where there were an equal number of PC's and Mac's. I used a standard PC font in my resume, but for some reason, the verson of Mac OS they were using at the time didn't support it so my resume didn't look formatted. This was way before the Intel Mac's were released.

After that, I always gave my resume in Word AND PDF format. The next place I went to was also a PC and Mac environment. This time my resume looked fine and I was hired.