Usually the vigorish on those payments are so high that you wouldn't do it for the purpose of earning miles. We discuss it every year around tax time: occasionally there is a promotion that makes it almost a break-even proposition, but I've never personally seen a slam-dunk good deal using a CC to pay The Man via one of these services.

A 5,000 Starpoint bonus might make me bite, but somehow I doubt they'd ever allow such a promotion to be structured to my benefit. They'd tier/threshold it in a way that I was always overpaying for the points.