Teaching Students Grammar -- Useful Y/N?

Over at Bardiac's place she wrote a post about strawmanning -- the ridiculous perceptions of what professors do and how we teach (or ought to teach).

In my comment there, I kind of went off on a tangent, orthogonal to Bardiac's original point. That tangent is one I'd like to take up here.

Grammar in the Slammer

This one comes to you from one of my students.

Very slightly NSFW.  (Cartoon vulgarity!)