I don't think I have ever recommended a cleaning product, but Gale and I recently discovered a dry powder called "Capture" that has cleaned the worn traffic areas off of some of our carpets. The product is made by Millikan, a carpet company and it's sold at Lowes and other similar stores. A starter kit sells for about $18 and included the 'activating spray' the powder and a brush...you supply the broom handle for the brush and a little bit of elbow grease.

Its simple to use...just spray the soiled areas lightly then sprinkle on the powder and work it in with the brush...wait 30 minutes and then vacuum it all up...carpets are clean, dry and best of all, they don't seem to have a residue that attracts dirt again

A larger spray bottle of soil release and a larger can of the dry powder is also available, but I would suggest staring with the start kit first to see if it works for you.

One more thing...this is a totally unsolicited article...just wanted to share something that seems to really work!