I used ChemDry last year: Positives they did very good work on mud type stains (dirt from shoes) and good on other areas.
This year I tried to use them again. I had a cancelation and they had to come twice, but in a few areas the carpet had heavy use and was quite dirty. It looked great after the job was done. The upstairs carpet looked great as well but felt a bit dry.
I will use them again next year.