From the YOSE site:
Permits to hike to the top of Half Dome are now required on Fridays, Saturdays, Sundays, and federal holidays when the cables are up. This is an interim measure to increase safety along the cables while the park develops a long-term plan to manage use on the Half Dome Trail.
Beginning in 2010, all people using the Half Dome Trail above the subdome must have a permit in possession on Fridays, Saturdays, Sundays, and federal holidays when the cables are up. A maximum of 400 permits will be issued each of these days. (Before the permit system, fewer than 400 people used this trail on weekdays, while about 800 people used this trail on weekends and holidays, on average.)
Beginning in 2010, all people using the Half Dome Trail above the subdome must have a permit in possession on Fridays, Saturdays, Sundays, and federal holidays when the cables are up. A maximum of 400 permits will be issued each of these days. (Before the permit system, fewer than 400 people used this trail on weekdays, while about 800 people used this trail on weekends and holidays, on average.)
