What is the difference between dimmable and non-dimmable CFL bulbs?
Do not use a non-dimmable CFL with a dimmer.  It shortens the CFL's life, and, in rare cases, a dimmer operating a CFL could result in fire.  Change it out with a switch to be safe.

Dimmable CFLs aren't as good as incandescent for dimming.  Their lowest settings are nowhere near that of incandescent, but they are good if you want the option to save on power and still be able to dim the lighting.  Sometimes you will have to turn up the light to get it to kick on and then dim it.  They can also be audible at their lowest setting.  If you buy some, save the receipt as you may not like their drawbacks.