David buschur took his off. The air pump will run for ~90 seconds max or until the coolant temp hits 150. Basically, it adds oxygen to allow fuel unburned in the cyclinders to ignite later and heat up the cats faster. Older STI's did not have these as they were the fleet exempt vehicle. WRX's didn't have these but instead had a pre-turbo cat. The airpump replaces the up pipe cat and, for the sti's, I guess they had to meet tighter emissions.
There is no performance benefit besides losing the weight of both valves and the pump.
Dave said he wouldn't make plates unless he got at least 15 people. I made up a "guaging interest" thread for him and we got 9 people, but then the thread was deleted for whatever reason.