I went to MK later in the day yesterday and it wasn't too crowded. No wait for Haunted Mansion, 10 minutes for BTM, 1 hour for Splash Mountain, 35 minutes for Buzz, 30 for Space Mountain while I was there.
It was, however, very hot. They are forcasting low 90's all week and due to the high humidity the heat index is 103ish. Bring the fans and water bottles.
Osceola heads back to school on Monday, Orange on Tuesday so any effect they are having on attendance will be over then.
We are off to Epcot...