Borders.com has knocked off perennial champion Amazon.com by the slimmest of margins in the latest PowerRankings of online book sellers by Forrester Research, Inc. (Nasdaq: FORR). Forrester PowerRankings combines survey data from online consumers and unbiased shopping tests to provide objective rankings of the leading US eCommerce sites. The companies ranking behind Borders.com are Amazon.com, barnesandnoble.com, and buy.com.

In a tight three-way race, Borders.com edged out Amazon.com by less than half a point, while third-place finisher barnesandnoble.com was close behind. The three split the top scores in various categories: Borders.com won transacting, cost, and delivery/returns; Amazon.com was tops in features; and barnesandnoble.com finished first in usability and customer service.

“While Borders.com only won by a tiny margin, the win demonstrates that Amazon.com’s advantages over the competition are diminishing,” said Tom Rhinelander, senior analyst at Forrester Research. “For example, in the spring PowerRankings, Amazon.com won in four of six categories. This fall, the company only had the top score in one area — features — which is one of the least important aspects according to consumers.”

Attention to site detail helped Borders.com triumph. Unlike Amazon.com, Borders.com states whether an item is in stock and posts the order total before asking for a credit card. Amazon.com still offers the most features, including the quickest express shopping, but phone calls were answered slowly and inventory information remains vague. barnesandnoble.com offers excellent search, but the shopping experience is marred by irritations like the inability to cancel orders without contacting customer service. While buy.com’s site constantly improves, it still doesn’t offer gift-wrapping and its email system was frequently down.

For the latest PowerRankings, Forrester surveyed 20,000 consumers from the NPD Group’s online panel. These consumers identified the most recent eCommerce sites that they purchased from and rated their experiences. A team of Forrester shoppers then evaluated the shopping experience for sites with a statistically valid number of consumer respondents, performing a series of rigorous tests. The consumer data and Forrester shopper scores were then synthesized and weighted, with consumer views accounting for two-thirds of the overall PowerRanking. A complete set of PowerRankings results — both consumer and Forrester shopper data — is made available to all ranked companies at no charge.

In the coming weeks, Forrester will be announcing results in additional PowerRankings categories. Additional information about each of the categories, including a complete set of rankings and scores, can be found at the PowerRankings Web site — powerrankings.forrester.com.