In the fight for online privacy, the American Civil Liberties Union has chosen what might be an unlikely ally: Amazon. To recap: Amazon has for years skirted around charging state sales tax. And North Carolina, like Washington, is broke. So to recoup some of that lost revenue, North Carolina demanded info on Amazon's local customers, including their names and details of what they bought. Amazon declined to provide, and in April filed a lawsuit against the state, citing the need to protect its customers' First Amendment rights. The ACLU announced last week that if North Carolina doesn't back off, it will join the lawsuit. It's an ironic pairing, given that earlier this month, Amazon stirred debate among privacy advocates after Kindle users discovered that the e-reader's operating software was keeping track of the passages its users "highlighted." The info was compiled for a feature called "popular highlights." Users' names weren't displayed, but that didn't stop some critics from saying that Amazon had "stepped over the line." MSNBC's Bob Mason has reported that Amazon stores and retains info on users' reading habits. A court order is all one would need to determine the authors of the notes or the users who highlighted a passage, he writes. According to Mason, some users say that the info-sharing enhances the e-reading experience. Even if that's true, the more information Amazon hoards, the more attractive a target it becomes to anyone who wants to know the particulars of another person's reading habits.