If you take the catalyst (platinum) out of the converter it will not pass emissions testing. In some states even if you fail a visual inspection you will be ticketed.
There are a range of penalties. However in Yavapai Co. (nothern AZ) there is no emissions testing, as of now. Alot of people in town believe Yavapai will adopt emissions testing within the next 2 years.
I have actually heard a rumor from a friend with an Apex´i SAFC that he could lean out his fuel flow so much he could pass smog with no cat-converter. However the car ran TERRIBLE, but hey if they dont see the fuel computer you simply drive away and go back to your old settings and pollute away.