Our family was there from the 22nd through 28th. (March)
It was WICKED crowded, but we had a great time because we planned. Basically, we read the advice books (Unofficial GUide) and subscribed to TourGuide Mike.
Common wisdom to from all sources, books, online etc:
1) Get to the park early, go on the popular and/or slow loading rides first. Get as much done before the crowds show as you can!
2) Avoid EMH parks like the plague during holidays (maybe even if you are staying onsite)
3) Get fastpasses as quickly as you can
4) Eat at "off" times
5) Get outa dodge during the afternoon when the parks are a mess... relax for a few hours, then go back in the evening when people start to leave
6) Get some key gems from TourGuide Mike (I found a couple there that I didn't see anywhere else and they REALLY made a difference.) It costs around $20 to subscribe to his site, but that is nothing compared to standing around with a couple kids in a line for an hour... we rode everything we wanted and our longest wait was 20 minutes, most were less than 10)
7) This tip is mine... if you go during a busy time, you almost gotta stay onsite or WEST of Disney or you will be in TERRIBLE traffic. We rented a Villa at Emerald Island resort. PERFECT. $135 per night plus tax and cleaning for a very nice 3 BR Villa with a full Kitchen. We hopped on Irlo Bronson and took the unmarked west entrance road to Disney (Sherbeth road I think) and got to Disney quickly. We went to some activities in other parts of Orlando a few days (Spring training baseball, Medieval times...) and the traffic was terrible. Stay WEST of Disney OR onsite if you can.
We followed this pattern and had a great time.
The recipe for disaster is to go to an EMH park at 10 am or later... do that and you are almost guaranteed a miserable time. If you want to sleep in on your vacation, you almost gotta go at another time of year.
Ed