Posted: July 28th, 2010, 9:00 am
Well, the church will tell you that it is bad every time. And they are correct, it's currently illegal and therefore sinful. However smoking marijuana is the same as any other activity, that is to say NOT a sin in and of itself.
(1 Corinthians 10:23) "Everything is permissible"—but not everything is beneficial. "Everything is permissible"—but not everything is constructive.
However that is not to say that smoking is never a sin, it is sinful if you are breaking the law by smoking, causing a brother to stumble (that phrase gets it's own wall o' text), or if the Spirit inside of you (your conscience) convicts you and you feel that you are doing evil.
But even if it isn't sinful, it certainly isn't smart. As AD said it is harmful, it alters your one greatest asset, your mind and puts you under the control of foreign substances. So basically, marijuana while not necessarily a sin, is not a very smart thing to do and (i think) ought to be avoided.

Once again, thanks to the illustrious Genesis^^