Vehicles without cats smell horrible! Please be considerate of other people driving behind you and leave it in!

Removing the cat is not worth it unless you have a turbo car. Years ago I ran a straight pipe on my turbo 240sx and saw quicker spool time and more pull at WOT. I'm sure if I didn't drive like a maniac back then I would've increased FE.

A diesel friend of mine owns a Dodge Ram Cummins turbo diesel and a couple VW TDI's and he reported significant mpg and power gains from removing the cats. Can't remember the actual numbers.

In the end its not worth it in a naturally aspirated car.

And keep in mind that boosted cars need to run richer in boost to keep detonation out of the picture. The richer A/F ratio will quickly clog the honeycomb of the cat as well. Typically when boosting a car, if you don't mind richening up the fuel map for boost, then why is FE even on the radar? If you have the ability to alter your fuel map you should be looking to lean it out a little more knowing that you're going to be lighter on the throttle than what your car manufacturer's design team expected.

IMHO fuel economy and low emissions should run hand in hand.