For the record, I can basically eliminate the flicker (and improve the overall smoothness of the glow to boot), but there's a performance cost to doing so. On my system, the framerate drops from 60fps to 30fps when I use the flicker-free version (due to vsync, there isn't any middle ground, so that's not actually quite as bad as it sounds; it just means that it crossed below the threshold at 60fps). I've attached a patch if you want to try it, but I'm not sure we want to put it into the SVN because of the performance issues. We could add an option to the graphics menu that let the user select what level of glow-smoothness they wanted (ie. low, med, high) or something, if people think it's appropriate, at which point I would be more comfortable including the patch, since it would effectively be optional anyway.