I remembered reading one article about Plants vs Zombies, where the developer (I believe it's George Fan) has found a good balance for a tutorial. Basically, he incorporated them as part of the series of levels. In the first level, the field is simple, where there's only one lane to worry about with one plant (a shooter). The second level made more lanes available, as well as introducing another important plant (sun-spawning). The third introduces a bomb, and so on.
What I am saying is that tutorials can be a good tool to teach players, but it should at least be something that fits seamlessly into the gameplay. The most prominent example of this is Super Mario Bros.' World 1-1 level, in which every element in this game is to teach the player something.
Thanks for reading.