As with anything, marijuana can be addictive. And like Sandman says, a lot does depend on personality. It sounds like in your case, marijuana may have become addictive in a habitual sense, as it is something that you have come to intergrate as a normal part of your day. I think someone can do this with anything, and then possibly encounter difficulties stopping, because it is afterall, a change of lifestyle and daily routine. If you are really curious, just lay off smoking for a little bit and see how you feel. Marijuana can be psychologically addictive if the user's personality allows for it. (It also has been reported to have mild withdrawl symptoms like trouble getting to sleep, or fatigue, stomach pains. Though, the concept of marijuana being physically addictive in any way is usually quickly refuted by most tokers....as the symptoms for many either never show up or don't last past two weeks.)

I do feel, the more you smoke though, the harder time you will have stopping. I'd only become concerned if you felt like your marijuana use was obstructive to your life, but you continued to use it. I think that's when elements of addiction may become apparent. However, if you still enjoy smoking, and regard it in a positive light, this is most healthy.