I once swore that I would sign up to use every social networking and collaborative workspace widget that came along. The phenomenon has now outstripped my capacity to keep up with it. But this is a great idea, lead me straight to this case study from a librarian at Lucent: "Making libraries more delicious: Social bookmarking in the enterprise."
I've even beta-testing a site a friend is developing and ostensibly getting Amazon gift certificates out of the deal! Could be a career plan B: picky usability tester.