EagleFlier the problem comes, as Eurocontrol discovered last week, is when there are so many squawks that the track server is saturated and then just rolls over. It is possible to suppress them but this only happens after initial processing has taken place. It would be easier to filter them out using mode C info but this would often require making an expensive bit of kit that adds nothing to the enjoyment of gliders/ultralights compulsory. As most of this traffic doesn't venture or isn't allowed into the upper airspace the conspicuity codes are unnecessary as far as I was concerned however they are essential in the lower airspace as, despite the almost universal use of GPS, airspace infringements continue to be a problem.