The New York Times writes on the New York Public Transit System’s proper use of the semicolon.
The relevant sentence: “Please put it [your newspaper] in a trash can; that’s good news for everyone.”
The use of a semicolon in this instance is indeed correct, but I would prefer a period or an em dash. Either would add more punch to the final phrase.
And Allan M. Siegal, longtime arbiter of NYT style, is quoted as arguing for a colon: “The semicolon is correct, though I’d have used a colon, which I think would be a bit more sophisticated in that sentence.”