OK shoot me down if I'm talking bullshit here but here goes:

The answer to this depends on what you're definition of addiction is.

ASFAIK something is defined as physically addictive if you suffer withdrawal symptoms when you stop taking it. By this criteria pot isn't addictive.

There is also the category of psychologically addictive which covers gambling and other more controversial (in diagnostic terms) things such as shopping. As I understand it defining this is a lot more difficult not to mention controversial.

The question then remains is pot psychologically addictive? and how do we measure this. The first question is much debated (as is the later) - The answer to the second would (and is AFAIK) presumably be similar to the criteria of the first - can people stop without adverse (psychological) side effects. In my experience (and what I know (second hand) of the evidence) the answer is yes people can stop it and therefore no it is not psychologically adictive.

It can certainly be habit-forming but just because someone doesn't stop it doesn't mean they can't and habituation is not adiction . Others would disagree, though they tend to be morally opposed to drugs. To declare an interest here - yes I have and still do smoke pot. - Though I now do so only occasionally because i didn't like the habits I had built up around it and making that change was as easy as making that decision. Though if you wanted to play Devil's Advocate it could be argued the fact that I don't turn it down when its around evidence that Really I can't give it up and are therefore addicted.