I've been looking at Unofficial Guide crowd predications as we'll be down March 20 - 26 and will be visiting two of the Disney Parks. Their projections which are usually pretty good are that this is the official start of the heaviest spring break season, and crowds will be similar to the busy summer season and even as heavy as Christmas week on some days. I would expect especially with WWHP, that the Universal parks will have similar very heavy crowds for this period. Here's what I got off of touringplans.com (I subscribed to that for $10) to get the touring plans for the Disney parks which help so much, especially when there are heavy crowds. 9s and 10s are considered peak holiday crowds.
Sat, 12 Mar '11 9 AK MK HS Spring Break Season Begins
Sun, 13 Mar '11 9 EP MK
Mon, 14 Mar '11 10 EP AK
Tue, 15 Mar '11 10 AK EP
Wed, 16 Mar '11 10 MK HS
Thu, 17 Mar '11 9 EP HS AK MK St. Patrick's Day
Fri, 18 Mar '11 9 HS AK MK
Sat, 19 Mar '11 9 AK HS
Sun, 20 Mar '11 9 EP HS
Mon, 21 Mar '11 8 EP HS AK
Tue, 22 Mar '11 9 MK AK EP
Wed, 23 Mar '11 7 MK HS EP
Thu, 24 Mar '11 9 EP AK MK
Fri, 25 Mar '11 9 HS AK EP