4.0 V6 Exhaust Question?

Has anyone cut off their catalytic converter ( I know its illegal and bad for enviroment) and just ran like a flowmaster or magnaflow setup, from the engine to muffler to outside. Any problems or concerns?
http://www.flowmastermufflers.com/index.php?page=112
Also and want to add- pipes from engine to aftermarket exhaust, no cat

 

First up-There are two cats each side.
Second- When you say "flowmaster or magnaflow set up" what do you mean?? Pipes straight from the headers to a aftermarket muffler?? or the aftermarket high flow cats??
You'll need a O2 simulator at the minimum to keep the ECU in check. And if you got for a straight thru pipe you might have issues with performance loss....but I'm not sure. Exhaust scavenging is very important to these engines and if you clear out the pipes you accelerate the flow and that can hurt you.