We also bought my daughter a used car last weekend and the floormats were absolutely horribly dirty. Just three or four drops of Winning Colours, some water and a scrub brush and they look brand new.
I'm replacing my AC evaporator in my Jeep now (just taking a break...) and it involves me completely removing the interior/dashboard/instrument cluster all the way to the firewall. I noticed I have about 11 years worth of dirty carpet, some maybe I'll post some pics/videos cleaning it up later today. This is about a 6 hour job, ugh. But if I want A/C during the 100 degree midwest weather, guess it's worth it.