We were there during the Easter season of 2000. It was VERY busy. However, the landscaping during this time of year is BEAUTIFUL and we really liked the Easter parade at MK.
As many have already posted, be sure to have a list and touring plan (from the Unofficial Guide if possible) of the things that you want to see. BE SURE TO HIT THE PARKS 1/2 HOUR BEFORE OPENING. The first hour (maybe the first two hours) are the BEST time to tour during peak seasons such as this. By 10:30am the parks become so crowded it's hard to walk.
Make sure to get your dining reservations made ASAP. If you wait until you're at WDW, many places will be booked up already.
Also, keep in mind that large crowds and long lines make folks very cranky. Even if you don't get upset, those around you might. If you go with the mindset that cranky folks, long lines and big crowds aren't going to get you down, then that's half the battle.
As was stated before, a crowded time at Disney is better than being at home.
Have a great trip!