The other day, the first review of Getting Lucky appeared on Amazon. It's a good one, so I posted a "Yahoo" to the Internet Writing Workshop. Several members responded by saying they were ordering my book, and between March 26 and March 28 my Amazon ranking increased by 474,377 places!
Those rankings are mighty volatile, of course, but such a big gain is a sight to see. It shows how getting and leveraging one review can make a difference.