Hundreds of gay-and lesbian-themed books suddenly disappeared from Amazon.com's rankings over the weekend, causing an uproar among authors and activists who alleged it was a stealthy extension of the company's policy concerning adult content but which the internet bookseller has dismissed as the result of a technical "glitch."

Some of the titles reported to have been dropped were back on the rankings, including Annie Proulx's Brokeback Mountain. Not all gay/lesbian works were dropped. There is also no comprehensive list (yet) of the affected titles, and some reports of outed titles contradict others

But clearly the pages of some books with with gay but no particular "adult" component have been shorn of their metrics.

The Mayor of Castro Street: The Life and Times of Harvey Milk, for example, no longer has a sales ranking, nor does Amazon list any longer the categories in which the book about the assassinated, open-gay San Francisco activist politician is popular (see blow). But as recently as April 7, according to a cached Google page, the Randy Shilts-penned biography was ranked 7,923 overall and was the most popular book in both "Gay & Lesbian >> Biographies and Memoirs" and all non-fiction books about local government. It was #4 in all books about the history of California.

Amazon's initial and only response has been to say the cause was technical, not editorial. "There was a glitch in our systems and it's being fixed," Amazon's director of corporate communications, Patty Smith, said in an e-mail to the Associated Press Sunday.

But word of the incident went viral quickly, and it seemed few were buying the innocent explanation. A Twitter hashtag, #Amazonfail, is now the top trending topic and a site has been set up to filter #amazonfail tweets and facilitate discussion around the sales rank issue. People have also begun tagging books on Amazon with "amazonfail" so all de-listed works can be easily located, and there's an online petition protesting "Amazon's new 'adult' policy."

One author says he's been having this fight with Amazon for months. Craig Seymore, Associate Professor of Journalism at Northern Illinois University, writes on his blog that he noticed his Amazon.com sales rank disappear back in February for his memoir All I Could Bare: My Life in the Strip Clubs of Gay Washington, D.C.

But he also noticed that Diablo Cody's (hetero) stripper memoir Candy Girl: A Year in the Life of an Unlikely Stripper was not removed from the rankings.

Seymore says his ranking eventually reappeared after weeks of discussion with Amazon reps, including one which told him his book was deemed adult content.

Author Mark Probst noticed that gay romance books like Transgressions by Erastes and False Colors by Alex Beecroft being removed and claims he was also told that they were removed because of adult content. But he points out that Playboy: The Complete Centerfolds was not affected.

The LiveJournal community MetaWriter is keeping track of titles that have had sales rank removed, and it includes a wide range of topics.

"Glitch" or not this is a fresh example of the new challenges to brands posed by social media, which can be a great marketing tool but can be used just as easily to bring them down. We're betting Amazon's last word can't be its last.