Whether the Mayan’s were right about the end of the world thing or not you’re still going to need a permit to climb Half Dome via the cables in 2012.
Yosemite National Park will require Day Use Permits seven days per week for climbing the Half Dome cables during the summer 2012 season. This is an extension of the interim permit system that was implemented beginning in 2010. Permits will be required seven days per week to ascend the Half Dome cables. This is part of an interim program designed to address crowding and safety issues on the cables. (via NPS)