Can you put a dimmer switch on compact fluorescent light bulbs?

I have but if dimmer is on low the light fixture sometimes "hums", can be anoying It also shortens the bulb life, significantly in some cases. But their are also CFL bulbs built to be used with a dimmer switch that avoid these problems.
Another Answer
You should only use CFLs specifically-designed to be used with dimmers in circuits controlled by dimmer switches. There is a proven danger of fire hazard when ordinary CFLs are controlled by dimmer switches and, so, this should NEVER be done.