I'd say it's made a change, at least at the MK. Last Sunday was very crowded, presumably due to early entry. Pirates had a posted 40 minute wait, Jungle Cruise FP return was +2 hours, all at 11:00am. Splash Mountain and Big Thunder were also similarly crowded. We hit the MK early, and did a ton of rides, but man did it fill up fast. We had the same experience the previous Thursday, on MK early entry day. After that, we decided the better plan was to skip the park with EE. This worked well, we went to AK on Saturday (instead of Friday, as previously planned) and met pretty reasonable crowds.
If you can take full advantage of EE (i.e. get at the park about 15 minutes before the EE opening time), then I'd say go and ride everything you can until about 11:00am, then get the heck out and hop to a different park. If, however, you're like me and discover soon after you arrive (like, on the first morning after you arrive!) that you'd much rather sleep a little later, and not wake up at 6:45am to do EE, then just start your day in any other park. Whatever you do, don't go to an EE park after noon unless you can't help it (the exception seems to be Epcot... it's so big and stays open much later, it thins the crowds after 5:00pm or so even on a Wednesday EE day).