I've been running mine with both cat's gutted for a few months now. I put a spark plug extender on the O2 sensor to get it out of the exhaust stream and it seems to work fine with no CEL. BTW it sounds better and it might have a little more pep to it, it is a manual though so it's easier to notice the little things.

2001 Sportage, TJ 106's, Everet spacers and bumpstops, Bilstein shocks on the rear, cone filter, Crager wheels, 235-75-15 Goodyear tires. Custom front winch bumper by Dave Scott. Currently DOA, but it is a work in progress.
2011 Kia Forte EX