The dash is like the Wild West. As a writer, I know I overuse it. I also use the sentence fragment on a regular basis. Author and grammar watchdog Lynn Truss of NY Times Bestseller "Eats, Shoots and Leaves" states, "The main reason people use [the em dash], however, is that they know you can't use it wrongly--which for a punctuation mark, is an uncommon virtue." 

The Chicago Manual of Style and the Oxford say there should be no space before or after the em dash, but the NY Times Manual of Style and the AP put it there. I'm a Chicago person myself.

I overuse the dash. I write satire. So, I'll have to say--and I mean this in all honesty--my conscience rests peacefully at night. 

In cooking a "dash" is something used sparingly. So should it be with writing.

Oh, that's a classic smackdown. I'm going to use this since I'm writing about this today. Not a bad smackdown from a math guy, I must concede. 

Thank you. I shall take a bow!