News from Supertopo.com is that "in order to enforce the Camp 4 time limit more effectively (and thereby enable more people to experience Yosemite), the campground office is tracking visitation in Camp 4 with a computer system. As of..well, now, in order to stay in Camp 4 each camper must provide a valid photo ID (Driver's license, passport, etc.), phone number, and address. Once you have stayed in the Campground seven nights (any seven nights over the course of the summer), that's it, no more. Sorry, time for someone else to enjoy the Valley." Previously, it was common behaviour to sign in under different names to get around the 7-day limit.