[itsdrewmiller]

I really don't think it is very many. There are clear patterns of failure for fizzbuzz - the biggest is the "copy-paste programmer" who sees a blank canvass and just has no idea where to start. Then you have your people who can write conditionals but can't reason about them - they will very often end up with a solution that compiles, but always prints the number no matter what, or never prints FizzBuzz, or some other obvious error that should be apparent on a quick review of ones code. Most of these people also take 10-15 minutes to write it out, where competent programmers consistently bang it out in five minutes or less. (And yeah, some of them probably know it by heart by now. Oh well.)

Screening someone who just absolutely can't program at all is, IMHO, by far the worst part of technical interviewing.