For reasons that are not relevant for this question, I went to several interviews at multiple companies in the past few months.
What I noticed is that, in the vast majority of cases, interviewers have absolutely no idea about what's on my resume. They just print it out right before the interview and bring it with them.
I reached this conclusion by mentioning very significant aspects about my work history and / or extra activities and getting genuine surprise emotions in return:
Oh, that's so cool, I didn't know you did that.
I'm referring to multiple and diverse types of information, all of which are clearly visible on my resume.
There was almost no interview in which I didn't experience this. So, my question is: why does this happen ? Reviewing a resume for 5 - 10 minutes for each candidate you're going to interview shouldn't be that big of a time consumer and it actually gets you more prepared for the actual discussion.
EDIT. A little clarification: It's not like I expect them to memorize it or anything. Just skim through it for 5 minutes so that you won't look so surprised if I tell you that I write in a technical blog or that I actively participate on StackExchange or that I actually did work with your technologies in the past. It leaves me a really bad impression of you as a company and/or as an interviewer. Companies keep saying that they need applicants who impress them. Well maybe they should take their own advice once in a while...