I don't have anything that can (reliably) create .doc files that consistently view the same in MS Word as they do in the application I've created them (I create and update my resume in Pages on the Mac). Creating a PDF means I know what it'll look like when they see it.

I once sent a .doc file to a potential employer, and when I arrived for my interview I saw that the font it had fallen back to (since it didn't have the exact one I'd used) was an aliased version of Courier for some ridiculous reason. It was ugly and difficult to read, the spacing was entirely incorrect, and it was generally a mess. If I were an employer and received a resume that looked like that, I'd surely count it as points against them (though it's possible that accepting Word document resumes means that this happens frequently and you get used to it).

I don't mind using MS Word at work, but I don't use it at home and have no intention of paying for it, so being able to provide someone a reliable, working document is not a guarantee unless I'm using PDF.