Even when turned on and off frequently, a CFL uses less energy than its incandescent equivalent. While there is a brief surge in energy use when a CFL is turned on, with today's starting technology, that surge usually lasts about a tenth of a second and consumes about as much energy as five seconds of normal operation.
However, turning a CFL on and off more frequently will also shorten its life. Because of this, and because CFLs are more expensive than incandescents, we generally recommend that consumers use CFLs in applications where they are on for at least fifteen minutes. This is where CFLs have the biggest impact and make the most sense economically. More on ENERGY STAR qualified CFLs.