OK, my wife (who is 27) is being referred for one of these. She has chronic pancreatitis. She has been on a high level of morphine based oral tablets for nearly five years now.
We are told the pump holds a small amount of morphine, which is inserted in a pocket in your abdomen (not to easy to get robbed). The morphine then transfers down a catheter to the desired infusion site. When it starts to run low, your hospital tops it up.
Regarding getting addicted, we have always been told, as long as you're taking it for it's intended purposes, you do not become addicted in the same way as someone who does not need it (however, you do become dependent on it).
Also, through this method of infusion, the amount of morphine required is less than what you take orally, as it goes directly to the desired location (thus, the side effects are less severe).
Also, I do hope she is not being referred for this as she is looking terminal! This is not what we're told. This is about as much as we know at the minute, as it's only just been suggested today.