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How I did it: I systematically went through my library and just kept plugging away. Purchasing the bar code reader was a definate help. Not much more to it than just finding time a couple times a month to knock off a shelf at a time.
Lessons & tips: don't look at your library and get overwhelmed. set little goals of just one shelf at a time. don't think you have to be super-disciplined to do it, do it when you want to, otherwise it will be more like a chore than fun.
Resources: The bar code reader that Library Thing offers for sale :)