Martin Schneider writes:

Via her mailing list, Mignon Fogerty, Macmillan's "Grammar Girl," passes along this "Ode to the Em Dash," written by punctuation enthusiast Sandra Ridpath:

"Ode to Em—"

As you dash about, I admire how
Straight, crisp and lean you look;
And whether before, after, or between
Your words, phrases, and clauses—
You create bold—almost brash—pauses.
Your sharp, double-sided sword either
Interrupts, explains, or provides a crisp refrain—

Your more subdued and delicate cousin Comma,
More delicately shapes her conversational stance.
With a classic hook, an almost unstated elegance,
She crooks her tiny tea cup drinking finger and smiles,
While you slash and grin like a pirate defending his men.
On all matters of meaning, movement, and patterns.

I'm not lean, bold, or brash, but I accept the vicarious compliment nonetheless. Nice job!