The week before and the week after Easter are two fo the busiest of the entire year.
We went the week prior to Easter this year and here's what I learned.....The crowds are thick but not horrible.  The temp is awesome.  The service outside WDW is the worst on the planet, especially the airlines.  Because they just dont care if the tick you off, theres someone else waiting for the chance to give them your money.
If you go, stay on property in a Disney hotel.  If you ever considered driving, this is the time to do it.  If you fly, arrive very early to be sure you've got your seat (this is a great oppertunity to score vouchers by volunteering to be bumped).  Dont rent a car from National.  Be sure your buy plane tix from the airline that is actually flying the plane.  ********.net was the one non-disney service that we found exceptional, so go with them for airport transfers.