For a while (not sure if they're still doing it), they were checking IDs for multi-day ticket holders at Disneyland in California (no fingerprint readers there). It slowed the lines down massively. I've been to both parks many times, and the fingerprint readers are immensely faster than checking IDs. For annual passes, they scan the pass and your picture comes up on the screen, but that's not as practical for a 3-day ticket.
I'm guessing an automatic ID reader is a lot cheaper than a fingerprint reader. Most long-distance buses around here have them, so you don't have to bring a ticket (just book with your id number).
It might be easier to spoof an ID reader, but I bet it would be hard enough to seriously hamper the second hand market for day passes at least.
