There's not doubt that Folex is good stuff, Autopian Grouse has a few really good carpet cleaning threads around here, and in a couple of them he recommends using Prochem Ultrapac Trafficlean as a pre-spray, and then Liquid Slurry as an extraction detergent, followed by All Fiber Rinse to finish up. That sounds like a lot of steps, but the chemicals work so well and so fast that it doesn't take much time to use all three chemicals. And the chemicals are *cheap*, too. One gallon of Liquid Slurry will make over 600 gallons of highly concentrated extraction liquid.
The Prochem chemicals blew the doors off Folex in cleaning the nasty carpets in my parent's rental house. One of the renters (there was a total of four college boys renting the house) was an auto mechanic, and he had no problem with walking all through the house with car grease/oil/etc on his shoes. The prochem stuff made quick work of all of it.