If you think of a 100w bulb, it uses 100w all the time. If you put a dimmer on, then it will use less power when the bulb is dimmed (the dimmer does not get hot, and the bulb is dimmer, therefore less power is used). The dimmer will never result in more than 100W being used for the 100W bulb.
Once upon a time, dimmers acted as rheostats (and got hot) an effectively wasted energy when the bulb was dimmed. This is no longer the case.
I have not personally tried a dimmed CFL bulb so no idea what is available or how effective it it.