I've interviewed applicants for several developer and tech support jobs over the years. During the recruitment process you get pretty good at evaluating resumes quickly and efficiently. In general, I can decide in the first thirty seconds if the applicant is going to qualify for an interview or not. I don't mean for that to sound harsh or ruthless, but for any given position there can be at least 100 applicants so it's important to filter through them efficiently.
I've compiled the below list of my top "resume fails" in the hope that job applicants out there can avoid making simple mistakes which might get their resumes deleted.
Above all, the most important advice I can give is to make sure your application looks like it has been tailored to the position - which it should be. There's no point in lazily sending out the same application for every position; you almost guarantee that your resume will be deleted in those critical first thirty seconds.
Happy job hunting and good luck!