One thing that really annoys me is when I get an email asking for advice about pursuing a career in my type of work or something along those lines, I write a reasonably thorough response, and... Nothing. Not even a "Hey, thanks for taking the time to respond." Apparently what I received was just a form letter asking for a job. This sort of event, which I assume is not unique to me, really discourages taking the time to respond to queries.