Per the Shaw carpet website:
"An inexpensive machine may remove surface dirt but will not effectively remove the hidden dirt and particles embedded in the pile. Invest in a good vacuum cleaner to get the dirt you can't see and prolong the beauty and life of your carpet. To ensure that your vacuum will conform to the highest industry standards, make sure that your vacuum cleaner is certified through the Carpet and Rug Institute (CRI) Seal of Approval/Green Label Vacuum Cleaner Program. Visit www.carpet-rug.org for details and listings.
Shaw recommends using vacuums with a rotating brush or combination beater/brush bar that agitates the carpet pile and mechanically loosens soil for removal. Carpet with thick loop pile construction, particularly wool and wool-blend styles, may be sensitive to brushing or rubbing of the pile surface and may become fuzzy. In addition, shag (or cabled) styles with long pile yarns tend to wrap around the rotating brushes causing damage to the yarn. For these products, Shaw recommends a suction-only vacuum or a vacuum with an adjustable brush lifted away from the carpet so it does not agitate the pile. Be sure to test a vacuum with a beater/brush bar in an inconspicuous location before regular use, to make sure it doesn't produce excessive fuzzing."