Have any of you guys switched from cast heads to aluminium? If so did it make your car run cooler?

I don't know that it made it run any cooler, but it did make it run a little better. I have Trick Flow 23 Degree heads with a Comp Cams XE 262 cam. Plenty of torque and will get you up to speed pretty quickly.

Over all temp may or may not change. But the temp in the combustion chamber will drop a bit. This can often be enought to eliminate the EGR valve, and cut NOx production. This can allow you to be a bit creative with other settings and adjustments. They cost, but they do help.

its been my experience that you can gain about 3 degrees timing all things being equal

Like Ken says, cylinder temperature may drop slightly to allow for other tuning options.

In theory you would think that it would drop the temperature of the engine. No different then using an aluminum pan vs a cast iron pan on a stove. The aluminum will actually heat up quicker, but dissipate heat quicker as well. Engines dissipate heat in two ways outward to surrounding air and internally through the oil and coolant. Aluminum heads just make it easier to pass heat between air and fluids. Thats the reason you can typically run half point or more compression with aluminum cylinder heads. One of the other benefits of aluminum heads are better flow and major weight savings in sprung weight.

If you want more engine cooling for less money then the aluminum heads then I would look at adding an engine oil cooler. With the right type of cooler (not the tube fin stuff) you can pull around 30 degrees out of the temperature of the oil.

You can also add on an electric cooling fan to the radiator, go to an aluminum radiator, or dual electric fans.