Some of my coworkers have sat on admissions committees for very competitive programs and they said it actually is kind of random. One of them said that one time, someone got an interview because they were a runner. I know it's tough because I've been on the receiving end of lots of rejections myself, but try not to take it too personally.
If you're still an undergrad, I strongly recommend working in the industry for a year or two, if the worst should come to pass and you don't get in anywhere. I've been told that a lot of programs look pretty favorably on people who are able to hold down a research job after graduation.