Deadlines. MIT has a number of deadlines throughout the year. Missing a deadline will cost you a late fee. Unfortunately, the system is not set up to let you know about pending deadlines and one often finds themselves first getting notified of a missed deadline via a late fee. They are listed in the MIT academic calendar. Here are a few examples:
Late Pre-Registration
Late Registration
Late Degree Application
Perhaps the ones that catch most by surprise are:
Pre-Registration for Summer Research (Even though you probably are not taking classes, you still register as a summer researcher: class 22.94)
Registration for Summer Research
Pre-Registration for Fall term (occurs at the beginning of summer).