We just returned on Saturday from a 10 day stay. I agree - go early.
In MK we rode the mountains, Buzz, Pirates, Peter Pan and Haunted Mansion all before noon.
In Epcot we were able to ride Mission Space (3X), Test Track, and Soarin (2x) before leaving at 1 pm.
At AK we rode the safari, ITTBAB, Dinosaur, Triceratops Spin and the rollercoaster all before 1 pm. We also had breakfast at Donalds during this time.
In MGM we rode the RNR (2X) and TOT before 10 am!!!
We took a break every afternoon and returned to the parks around 5 pm. But most of our riding was done in the morning. The crowds were definitely manageable - the heat was a different story!
As a side note, it is so helpful that my DH doesn't ride much. He is our official FP runner. We would ride and he would take our APs to get another pass. This allowed us to do more that the average visitor. For example, in Epcot my kids and I would go to MS and ride while DH got FPs for Soarin. Then, we would ride MS (again) and Test Track while he got another FP for Soarin. We would meet him at Soarin and get to ride it 2X - virtually back to back. Sometimes we would have to wait, but not often.
But the biggest hint - was given by zdad. Always get another FP when your current FP says you can!