At Disneyland, we would stagger fast passes (I think it was an extra $15/day or something per person) so we breezed through every line. Worth every penny. It's harder at Disney World because they do fast passes differently, but when I did it two years ago we had fast passes for every long line ride we tried to do. We did skip 1 or 2 because they weren't worth 2 hour+ waits, but we had a super full day. The longest we waited was at Universal for a couple of the Harry Potter rides.