Last time we went to Orlando we went for 14 nights and still didn't have enough time to see everything. Here's what we never saw last time - Blizzard Beach, Universal, Islands of Adventure, Busch Gardens in Tampa.
Sometimes we saw 2 parks in one day
Hollywood Studios and Epcot can easily be done in the same day
or Epcot and Animal Kingdom, do one in the morning and the other after dinner time 4pm+
The magic Kingdom however is so big I spent the whole day there.
I've been writing out a sample itinerary to see what all we can cram in. I wish we had the money to go for 3wks because then we would get to see everything and relax at the same time.