Been the past two memorial weekends. Early Entry is available. Usually, the weekend days are blacked out for most APs, but not Monday.
That said, "busy" is relative. Magic Morning hour is great! Easy to hop around DL and see just about everything. Lines are very very short or just walk on (Star Tours, Matterhorn, Peter Pan, all other Fantasyland and Tomorrowland rides). After that, it is busy but not bad at all...until evening.
Night time it is stacked during high-movement times (after Fantasmic, parades, etc), especially since there are constrictions created by the rope lines and cast members forcing traffic in certain directions. When I say stacked, I mean hold onto your loved ones and just keep baby stepping forward until you pass the high traffic area. otherwise, navigation isn't bad.
We enjoy DLR during this time, as crowds aren't bad (for us) and most everything is open.
On a side note, I love that Sat & Sun are blackouts for most passholders. Makes for lower crowd levels. In addition, we use the Mornings=park, afternoon=hotel, evening=whichever plan.
