Combining Human Knowledge with Machine Learning for Robust Data Flows

Many companies including Google, GoDaddy, Yahoo!, and LinkedIn use what's known as HITL, or Human-In-The-Loop, to improve the accuracy of everything from maps, matching business listings, ranking top search results and referring relevant job postings. Why are we still at this point? Because many times humans are better at labeling content than machines. However, when we combine human knowledge with machine learning, we can create truly robust data flows. With that being said, what's the best way to go about it?