We just returned from doing all four parks last week and were surprised at how crowded it was. Most travel guide books say early May is a great time to go because crowds are lower, so maybe our expectations were different, but we actually left MK at noon one day because lines were so long. The bellman at our hotel told us that several of the resort hotels were full.
Tip: If you are staying at a resort, don't do the early entry, or if you do, go for the first couple of hours and then go to another park. We found that whatever park had early entry was the most crowded that day.
If you have any questions feel free to PM or email!