When planning your Disney vacation, give yourself enough time to see everything you wanted to see. You can spend an entire week staying at a Disney Resort and still not see everything in all 4 parks. It's said in one of the guidebooks that to see everything there is to see, you'd have to stay a month.
I always plan for at least a day in each park. And if you're planning to go to one or both waterparks, you'll need most of a day in each. Downtown Disney won't take up a whole day and is a great place to spend an evening.
Also keep in mind that if you're doing any of the Disney Dining Plans that include table service restaurants, you'll have to allow for about an hour and a half for your table service meal. If you're going to a dinner show or a character meal, plan for a little longer.
Summer is a busy season in Disney and it also gets very hot in the middle of the day. I always plan a pool break after lunch during this time of year and then head back to a park late afternoon. This is especially helpful in giving kids a much needed break from the heat and everyone returns to the parks feeling refreshed.
Also remember that there are other activities that take place in the parks or at the resorts that you may need to allow time for. Bikes and horse-drawn carriage rides are offered at some of the resorts. Small boats called Sea Racers can be rented by the half hour and are available at several resorts. There are arcades at most resorts and some vacation packages now include a 30-minute arcade card.
Whether you like to vacation at a fast pace or a slow one, you can keep yourself very busy in Disney if you're there a week. And if you don't see everything you wanted to, it's always a great excuse to go back!