Prior to Facebook and Foursquare, Folkman was an engineer at bit.ly, AOL and Betaworks. He also holds the honor of being the only employee to have ever left Foursquare (for Facebook last November), Foursquare has verified with me.
“[Folkman's] expertise in building highly scalable technology in mobile, social, and location will be invaluable to Path,” Morin said. “His specific expertise in MongoDB is especially important as we are helping to pioneer document-based data structures at scale, the best way to store and access social and location data.”
We’re also hearing that Folkman decided to leave Facebook and then approached Path. Path of course was founded by former Facebook Platform Manager Morin. The two did not overlap at while either was at Facebook.