IMHO the best way to have your robot measure distance to objects. Fast and accurate.
If you are using Picaxe, you may find this info useful: http://letsmakerobots.com/node/66
DAGU made a holder for us. It can be used as Pan / Tilt or just as Pan or Tilt:
Oh, and note that if you use it just as Pan, you can mount the sensor on the inside, so it is working from above the center of the servo horn.