jump does not give any more speed, but due to some imperfect math in the q3 (and many other) engine, strafing while jumping will make you go slightly faster, and if you jump at the exact moment you hit the ground, you will keep that speed and your next jump will make you a little faster again. tremulous appears to cap the speed you can gain using this method to keep it from becoming rediculous, but the difference is still noticable (if you want to get really fancy, you can read up on circle strafe jumps)