There are a few places that require a deposit - CRT and California Grill come to mind - but that is not the norm. If you have a meal that requires a deposit, they charge you a cancellation fee if you don't come. However, if you are on the dining plan, they will use the dining plan credits instead of charging you for the meal on the credit card when you actually go eat there.
Victoria and Alberts at the Grand Floridian requires that you dress up. There are a few places with a business casual dress code (i.e. nicer shorts/pants with collared shirt for guys or skirt/jeans with nicer shirt for women is my understanding, but maybe it's written out somewhere), but the only ones I can think of are Jiko, Flying Fish, Citricos, California Grill and Narcooses. There might be a few others, but they are only in resorts. All theme park restaurants are fine with standard theme park attire and totally casual.