Bumped into this DVI/PDF previewer today. I have always been complaining about the performance of MacGhostView, which is unbearable. I almost pulled out the source code of GV and compiled an X11 version. This TeXniscope thing seems pretty fast, even if it converts PS to PDF using an external distiller. I don’t have anything against PDF, but I just use PSTricks, so that I have to rely on PS.