Many schools in SE had that week off last year, we went and it was crowded. Was the same in 2002 and expect the same in 2007 Wasn't as bad at Universal Parks. We are going again this year for the entire week because we are out until the 8th. Also (1) many Euro schools have a longer holiday than we do and you will see those families as well (2) Marathon and Half Marathon split to different days allowing more runners as of last year, so the number of racers is somewhere in the 30,000+.......that will be the 5/6/7th including the Family 5k on the 5th.
I go expecting crowds and if they are lighter than it's a bonus.