Not in the sense that it is labeled that way and alchohol and cigarrettes are not. As soon as you start doing stuff you've been told not to, the trend may or may not continue. Weed is not a gateway drug, people just get a gateway mentality.
Imagine that smoking weed is a widely accepted behavior. If someone takes up that habit, they have not yet crossed the "bad behavior" line and would likely not continue to experiment (except with maybe tobacco because of their similarities). Just the same, imagine that you grew up hearing, "Don't drink soda and alcohol." Those who try soda and like it will likely also try alcohol. Weed becomes a gateway drug because it is illegal, once you get into the "illegal territory" and enjoy it, you may continue to the next thing.
As a side note, many pot smokers have a firm opposition to any substance altered by man including OTC pain relievers. I find that most people who experiment and are able to come out of their bad habits will tell you that weed was the one thing they didn't really regret.
I would have to agree with an above post, alcohol is more likely to cause you to engage in stupid behavior which you would otherwise avoid.
I wish we could just shake the brain wash out of the world. Maybe jail wouldn't be such a thriving business then (yes, jail is a HUGE business).