I'm actually in the same boat. Going the week of the Mar 20th. I keep thinking that it won't be AS crowded due to Easter being late that year. However, in the Unofficial Guide they rate the week of the 20th and 26th a 10 on a scale of 1-10 for crowd levels. Only one other week gets a 10 and that is the week btwn Xmas and New Years.
I'm keeping my fingers crossed that it won't be that crowded, but I'm planning for the worst in the meantime. We are bringing our best friends for their first visit. Our 4yr DDs are bests friends and TOTALLY into the Princesses. So I'm getting all my touring plans down now from the touringplans website and TourGuide Mike to ensure they have a good time. I don't want their first trip to be remembered as standing in lines all day.