I'll rephrase my position a bit...
Removing a modern, relatively low restriction, and functioning catalytic converter will have minimal gains and cause a lot of extra pollution. A non-functional and clogged one however will throttle the breathing of your car and make it run poorly and pollute more heavily than no catalytic converter at all.
The catalytic converter's now are a much better design than those in the 1990's. We build them at work so I know. The Buick one was about 40 pounds of outdated, stamped metal design, before it became clogged. After it became clogged it was more like 60 lbs, and resulted both in the much loved rotten egg smell as well as the car running so rich you could smell the gas coming from the back. The Buick catalytic converter was also followed by a u bend to protect the rear O2 sensor. The u-bend is a crimped piece of pipe that reduces exhaust diameter to about 2", this was the choke point of the exhaust for those cars. A bolt on cat-less down pipe eliminates this, is less restrictive, less prone to failure, as well as significantly cheaper than one with a converter. Replacing the entire unit with one mandrel bent piece gained quite a bit of power and lost a lot of weight. It also returned about 3 mpg that had been lost. That was why I made my decision.
The Eclipse's front catalytic converter mounts had rusted through... so It wasn't doing anything anyway due to the exhaust leak. The test pipe was a package deal with the headers and made the install and repair faster. It is also 304 stainless vs the original mild steel design and of much higher quality.
I am definitely not a hippie, I do care about the environment. My part in it is by not buying new cars. Some other guy takes the depreciation hit, the car stays running longer, and the pollution from manufacturing is reduced. :D Perhaps I care more about money than the environment. My buick has 260,00 miles on it. The eclipse just gets 10 more mpg, so its the daily driver.
Edited by cheapfi - 11/5/12 at 4:10am