We were at US last July (staying onsite) and switched to WDW (CBR) on the 4th. We saw many unhappy people at US that did not do their research, did not arrive early or stay onsite or purchase an express pass. Those folks were encountering lines exceeding an hour on all of the popular rides at both US and IOA. I really regretted switching to WDW on the 4th as although the atmosphere and fireworks at MK were nice, the crowds were overwhelming and we truely missed having fotl. US/IOA is fine if you are staying onsite, if not, and if planning on visiting WDW, make it a pool day instead.