Jon Udell is working on a cool tool for this.
Why would you want it? As Dave Winer said, when he and Andrew Grumet created a script to find people who share your RSS subscriptions, “Think of it as your personal echo chamber.” Your bookmarking doppelganger probably links to webpages you haven’t found yet–but will holler “Wow!”, “Wee doggie!”, or “W00t!” when you do.
Jon Udell plans to compare user profiles from the popular shared bookmarking site Del.icio.us. (Not surprisingly, his announcement has attracted a lot of bookmark action from folks who use Del.icio.us, including betsythedevine.)
So you have to share your bookmarks before you can find out who shares them with you. For some reason, this reminds me of one of my favorite Kevin Marks quotes from Bloggercon 1: “I realized that I can read thoughts–but only if people write them down first.”