Does "usefulness" feedback on Amazon reviews matter?

I think that there is, but I'm not entirely sure, so I asked my friend and Amazon top 150 review Thomas Duffbert about it. Turns out he's just recently blogged about Becoming a Top 150 Review and here's what he shared:

"If you wonder how the ranking works... On the site, each review by a person has a "Yes"/"No" button after the review asking if the reader found the review helpful. Although Amazon doesn't publish the formula, common wisdom has it that a point is awarded for 3 positive votes and for 10 positive votes. There's a deduction for having more negatives than positives if the difference is multiplied by the square root divided by the cycle of the moon, or some such thing. Basically, the more positive votes I get, the higher I move up in rank.

So, if you *really* like a review you read over here, feel free to click through to the book on Amazon, find my review listed on the book product page, and vote Yes."

In case you're wondering, we're talking about this:

Notice on the top that this particular review was considered helpful by all three of the people who voted and that I can vote myself by clicking on the "Yes" or "No" on the last line.

(and, yes, this is an excerpt from a review for my popular Wicked Cool Shell Scripts book :-)

Hope that helps clarify what this is used for. IF you want to learn more about the Amazon reviewing system, you can spend hours exploring the Amazon discussion boards, specifically this thread: Rubric for Determining Votes?