Some important facts:

• 85% of searches are more than one word.
• 25% of searches are completely unique and have never been seen before (4+ keyword phrases). [Source: Udi Manber Google's VP of Engineering]
• Analysis of eCommerce conversion rates are that 38% of sales come from 4 word phrases, and 21% come from three word phrases. However three word phrases have much higher traffic volume. [Source: Oneupweb Study]

Three word phrases are the keyword sweet spots, that deliver business, because they right mix of volume and conversion.

Relevancy is what delivers conversions….

Note: Conversion rates exclude “brand” searches, where single word phrases still delivery high conversion.