Don't know about CFLs, but I've looked into LEDs to replace some lighting where I work and from what I can tell, you'll have to get a special dimmer if you want LEDs. Everything I've read says that they operate at their most efficient and last the longest if fed a certain voltage (Or maybe current... I'm no electrician, so I may be using the wrong terms here) Standard dimmers only decrease the voltage, which works fine for a filament bulb, but can cause problems for LEDs.
The dimmer you need is called a "pulse width modulation" dimmer. It sends power to the LED in small pulses, so it's flickering on and off very fast, but at the proper voltage (or maybe current) each time.
The only PWM dimmers I've seen output 12 volts, so you'd need LED clusters that are designed for that. (They make little MR-16 style LED lights that would go into track lighting or recessed ceiling fixtures) The screw-based replacements all run on 120VAC and have their own circuits inside the "bulb" to convert it to the right DC voltage. I don't know if a PWM dimmer would work with AC current, so you probably can't dim the 120V clusters.
Right now it looks like you're stuck with what works in your existing fixtures, or you re-think the wiring and lighting layout in your house.
Here are some links to sites I was looking at:
http://www.besthomeledlighting.com/http://www.ledsmagazine.com/press/16462 (Press release claims that this new MR-16 style LED is fully dimmable, but it doesn't say how)
http://theledlight.com/index.html#24 (Some links to dimming info and wiring on this one.)
Be wary of LED clusters you see in a hardware store or big-box place! I bought a set of 3 hockey-puck sized clusters for $20 that were marketed as under-counter lights. (I was using them on an aquarium) They were nice and bright for a few weeks, then faded till they were unusable. They were probably being over-driven to make them brighter, or maybe heat dissipation was bad, but it caused them to wear out fast.
-Todd