SEOMoz uses AdRoll (disclosure: i'm founder) for retargeting. It's been a pleasure working closely with the Moz team shaping their campaign...
We help thousands of brands with retargeting and, yes, the results range from "holy crazy crap" to "hot diggity dangermouse." We offer an easy-to-use platform, great ROI, and powerful personalized advertising (eg, LiquidAds.)
Like secret_target says, partnering with a retargeting platform gets you much wider reach and better results than working exclusively with a single inventory pool like Google. (Google has the monopoly in search, but not display...)