Ok.. So what are they? For some ppl disabling them seems to fix crashes, etc? For some reason, it isn't mentioned in the manual either... Can someone fill us in?

From what I experienced in other Opengl games using Geforce videocards, GLextensions seems to significantly increase the framerate of games. In fact it even makes some games look sharper such as in Return to Castle Wolfstien. In most my other Quake 3 based games this option did seem to shut off vsync creating that dreaded tearing effect, but the framerate increase was worth it. Thankfully, in Jedi Outcast, the vsync stays enabled even with the extensions turned on.