I found a typo on my CV after I applied for my first program. Luckily I fixed it so it wouldn't be on my others, but I agonized over it for hours. Funny enough, that's the only school I've heard back from so far, so I guess the typo wasn't a big deal.
Biggest "mistake" was with my LOR. One of my professors who was writing a letter for me wouldn't respond to any of my emails the second Fall exams were over. A week after my first application was due, she finally emailed back and said she had a family emergency. At this point I had already asked another professor to write a back up letter, but honestly her letter would look so much better on my application. Throughout the entire application process all of her letters were late, even after I'd email constant reminders. Just saw this week that one to WSU that I thought was already submitted was not, so it's 2 weeks late. I've been told that a late letter is not the end of the world, but my biggest mistake was not getting a back up recommender earlier in the semester and trusting a somewhat absent minded professor to take care of such an important part of my application. Besides that I haven't looked over my materials. I know I'll find mistakes, but I guess there's some comfort in knowing that most of admissions committees will not be reading over my writing samples as intensely as I do.