Can someone explain what happens when you install the lower rating thermostat? I'm assuming from a performance standpoint, under certain conditions like moderate ambient temperatures, the intake air will be denser for better performance. Under summer conditions, is there any real difference though?
What about emissions and fuel economy. I'm just thinking that if this were such a good idea, the manufacturers would be doing it.

I installed a 180 to help keep engine temps under control. In the summer my car got close to the red line for heat frequently. Now with the 180 it seems to stay cooler longer. 180 supposeldy isn't as good for emmisions as a 195 but the difference in nominal. A cooler running engine may also help to get cooler intake temps with means a slight gain in HP. The main reason I do it though is to protect my engine from exesive heat, which kills engines (especially the way I drive ).

Is the T-Stat easy to remove the old one and install a new one?

Quite easy. Follow the upper coolant hose back to the engine and where the hose turns into metal you will see a small fitting to blend the block and hose together. There are 2 bolts on that fitting. Remove the bolts and the t-stat is right there. IT really is that easy. Just make sure you use a new gasket and seal it properly so it doesn't leak.

Do this on a COLD engine or be prepared to lose about a quart of coolant. Dont forget to bleed the system after the install and make sure you torque the t-stat housing bolts to spec (15ft/lb I think)

EDITED: Thanks Silver

Yea, definately when its cold! I plan on flushing the system out also. What happens if you tighten the bolts over the specified settings? Or do I even want to know

Over torque can cause a leak, also make sure there is no coolant in the bolt holes when you put it back together. Hyrdolock can give false torque readings and youll have a leak then also. The 00+ dont use gaskets but make sure you clean your old gasket off and get a new one.

Ok, I did get a new gasket also. Undertorque can also cause a leak or will it fly off? I dont have any special tools that measure torque, can I do it by touch and feel or should I take it in somewhere?

I'm not sure what the feel difference with a gasket is without (i dont use a gasket) but you can get pretty close with a socket wrench by wrenching until its tight then about another 90 degrees. You can rent tq wrehnches from autozone for not a whole lot of money if you want to have it done right.

Definitely use a torque wrench on any fastener that you depend on for reliability. It'* one of the best investments you can make if you plan on doing any work yourself and should last a lifetime if properly cared for.
15 ft-lbs for the thermostat bolts.