A jump in sales.

[EMARX]

I would be interested to know. After Mr King has given a book a positive endorsement like the ones in the article from the Boston Globe. How much does it boost the sales of those books. I'm sure someone has calculated it, but it would be interesting to see the actual numbers.

[Mr Nobody]

Could work both ways, though. SK fans are likely to give it a go. Those who dislike SK, for whatever reason, would likely avoid his recommendations like the plague, where they might otherwise have had a serious look at it.
I guess you'd have to know someone in the trade to get those sorts of figures, or else know how many copies had shifted in the week or month before the article or from the date of initial publication, and compare them to the same period after the article appeared. You'd probably also have to run a poll like 'Did SK's endorsement influence your decision over [X]?'

Of course, someone will now likely post a definitive answer that is widely available!