Facebook is poised to roll out "Friendship Pages" aggregating the online interactions between two people. The feature is a potential boon to jealous ex lovers and nosy gossips—and there's no indication you'll be able to opt out.

Facebook engineer Wayne Kao blogged about the feature late last week after helping to invent it during an all-night hackathon. The "Friendship Pages" show all "Wall" posts and comments between two friends, photos in which they are tagged together, events they've both RSVPd for and, judging from a screenshot Kao posted (below), friends they share in common:

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It's the sort of technology that could be useful and sweet, in the right context. Kao, for example, hypothesized using it for two friends who have "begun a new relationship, gotten engaged or gotten married."

But other Facebook users have imagined more sinister applications. ReadWriteWeb's Mike Melanson wrote that "Facebook Friendship Pages are Just Plain Creepy," calling them "the ultimate tool for stalkers, nosey friends and jealous significant others." On Forbes.com Kashmir Hill called the feature "a new and improved stalking tool... [for] jealous significant others, nosy parents, or reporters tracking down the identity of a Christine O'Donnell paramour."

But she also approves; the information used by Friendship Pages is already out there, after all, and no stalker or gossip worth his salt needs a special tool to put the pieces together for him. The most enthusiastic users of "Friendship Pages" should be privacy seekers trying to figure out how many clues they've left behind.

[Photo via Rishi Bandopadhay/Flickr]