I went during Mardi Gras 2005, and will be there again for MG 2006. I've also been during THanksgiving and peak summer time. MG crowds are large, but nothing compared to THanksgiving or Summer time.
Get there early, and you can hit all of the rides before they get crowded. We find that people stay out late, and don't get to the parks for the early times, but by mid day, the park that opened early is packed.