The National Park Service has expanded the need for a permit to climb to the top of Half Dome to all seven days of the week. (Before it was only required for weekends and holidays.)
http://www.sfgate.com/cgi-bin/article.cgi?f=/c/a/2010/12/15/BA2U1GQIQM.DTL
http://www.nps.gov/yose/parknews/hdpermits3.htm