Absorbed fuel lighters (zippos) and soft flame butane lighters have been allowed in carry on since 2007. NO lighters are to be in checked luggage unless in an approved DOT case.
Torch lighters have always been banned.
Q. Are lighters not a threat anymore?
A. Lighters are not a serious threat. Lifting the ban is a common sense, risk-based security decision. This change allows officers to focus on finding explosives and IED components. TSA collects 22,000 lighters a day.
Q: Why were all lighters banned as carry-on items in the first place?
A. In April of 2005, TSA began enforcing a Congressional mandate to ban common lighters on the secure side of airports or onboard airplanes.
Q. What is a torch lighter?
A. Torch lighters create a thin, needle-like flame that is hotter (reaching 2,500 degrees Fahrenheit) and more intense than those from common lighters. Torch lighters are often used for pipes and cigars, and maintain a consistent stream of air-propelled fire regardless of the angle at which it is held. Torch lighters continue to be banned.
http://www.tsa.gov/travelers/sop/index.shtm