Alexandra, the Disney early entry system shouldn't affect the other parks at all. I am still compiling notes on what the traffic patterns look like since the re-introduction of early entry, and elsewhere, and the picture is horribly vague just now. This currently is my best guess-timate at the likely scenario for the 7 main Orlando parks:
Mon: Busy - AK, MK; Less Busy - Epcot, USF; Least busy - IoA, SW, MGM.
Tue: Busy - MGM, USF; Less Busy - Epcot, MK; Least busy - IoA, SW, AK
Wed: Busy - Epcot, AK; Less Busy - IoA, SW; Least Busy - MK, MGM, USF.
Thur: Busy - MK, USF; Less Busy - IoA, SW, MGM; Least Busy - Epcot.
Fri: Busy - AK, Epcot, IoA; Less Busy - USF, SW, MGM; Least Busy - MK.
Sat: Busy - MGM, MK, USF, IoA, SW; Less Busy - Epcot; Least Busy - AK.
Sun: Busy - MK, IoA, SW; Less Busy - AK, Epcot, USF; Least Busy - MGM.
The usual rule about arriving as early as possible still applies (even more so these days, when you can have 2 really quiet hours in many cases), but I reserve the right to change my mind at any time!
In all seriousness, any feedback on this subject is always welcome, especially from Disney veterans who know a Busy day from a Not-so-Busy day! This remains a work in progress, and other factors (War in Iraq being the main one) will almost certainly have a bearing on business this year. So stay tuned, and don't forget to post your own reports here!
Simon.