With so many misconceptions regarding the best method of carpet cleaning, which should you use?  Instead of my opinion, let's go right to the source.  Notice what three of the top leading carpet manufacturers recommend as the preferred carpet cleaning method:


Shaw Industries
Shaws Choice: Hot water extraction
"Research indicates that the hot water extraction system provides the best capability for cleaning. This system is commonly referred to as "steam cleaning," although no steam is actually generated. The process consists of applying a cleaning agent into the carpet pile and using water in the extractor to recover the used solution and soil. This can be done from a truck-mounted unit outside the home with only the hose and wand brought inside or by a portable system brought into the home."
http://www.shawfloors.com/cms/Articles.aspx?DN=1129,1112,1106,29,4,Documents


Mohawk Industries
Mohawks Choice: Hot Water Extraction
"Even with regular vacuuming, soil particles and oily dirt will cling to the carpet fibers. With foot traffic these particles and oily dirt are driven deep into the carpet. We recommend professional hot water extraction every 12 to 18 months. Periodic cleaning, using the hot water extraction method performed by a professional cleaner, will refresh carpet appearance."
http://www.mohawk-flooring.com/caring-maintaining/carpet-care.asp#Cleaning


StainMaster Industries
To Maintain Texture Retention Warranty: Hot Water Extraction
"There are three key steps in a proper maintenance plan: Vacuum frequently, clean spills promptly, and have professional carpet cleanings at least annually. Remember, also, to maintain your texture retention warranty, you need to have a professional steam cleaning/ hot water extraction at least every 18-24 months."
http://www.stainmaster.com/carpet-care/carpet_care_faq.jsp

Pals Carpet Cleaning & Services method of cleaning is: Hot Water Extraction also known as "Steam Cleaning".