Honestly? Not as often as you might think, depending on how your resume is laid out. Often, information for a particular job is all lumped together so that it can be hard to tell what you did when, especially if your resume has gone through a staffing agency. And, as someone who's participated in a few interviews, asking details about the resume is like asking someone to do the FizzBuzz test. It's disappointing how often it trips people up, revealing that their resume does not match their actual experience.