Going back to the "positve and negitive" review. Let me sort of demonstrate my "buying process."
-> Did Monte Cook write it? Yes, then it is on the "Will buy" list
-> Did MC publish it but not author? Yes, then on the "Most likely will buy"
-> Is this some cool Licensed Setting that I am a fan of? (ie B5) move to "Fan Budget"
Now that the auto-buys are out of the way...
It now depends on the topic of the book. In general, a product that scores a lot of 5's from "trusted" reviewers will get a serious look by me. And i would consider buying it even if I had no use for it.
When I am looking for some type of new rule system (like Naval Comabat) I will shop around. See which style I like. I will use the reviews to get a feel for the product, but I may choose the 3 over the 4 simply becuase I liked one particular aspect of that book.
I think I start ignoring products that start getting into the 2 range. Unless it is one of my Auto-Buys. (but then rarely do my Auto-buys get 2's

)
So a 3 to me means. A solid product, but not something that I must have. Unless I am looking for information that it will be providing.
-gustavef