Not to start an argument, but I guess it depends on what your idea of packed is. We have been to WDW during spring break onour last two trips and it hasn't been packed.
It has been crowded, not a two hour wait that I remember, but with the use of the fast pass system and a good knowledge of what we wanted to see we really enjoyed ourselfs. Of course the major factor should be when is your spring break and how close does it fall to Easter. For us it has usually been the second week of March and Easter has been weeks away. The closer you get to Easter the more crowded it becomes.
We are taking our first Christmas trip this year and looking at the crowd indicators, it appears as if it will be close to what we have become use to during spring break.
At one point and time we use to take the kids out of school to go, but now that they are older we have quit that practice and now must go when they have their school breaks. I'll take spring break and Christmas crowds any day over summer crowds and heat. Trust me I have been there in July, along with all of Brazil, and will never do summer again.
Good luck, I think that you will find that it may not be as bad as some make it out to be.