Tips from last year:Make sure to pay close attention for the payment button when you are submitting your application. I made that mistake last year. The payment flow is separate from submission, and if you click through too quickly you will miss it. Read the instructions on every screen before you proceed to the next.
Last year there was also a character issue (since essays were copied in the application in text format, some characters came out funky on preview). We had to go through essays to replace double quotes with the right quotes, etc. Admissions was aware of the issue and they might have fixed it (and not held it against people), but this is an FYI for you guys, to help you avoid extra panic on last minute submissions.