Something I learned about at library school that actually struck me as new and exciting, was the citation index, which the professor described as a list of references more recent than the article they were referencing. At first I dismissed this as an impossibility, a Borgesian fantasy - an article citing articles more recent than itself? Impossible! - and it troubled me the same way seeing the picture of cover of a book inside that very book still troubles me. But with the professor's patient prodding (I was taken aside) and gentle explanation of the difference between "snowball searching" and "citation searching", the concept gradually seeped in. And then citation indexes began to excite me in the same way web2.0 and gossip in general now excite me; you know, getting to see what everybody is saying about things!!! During library school I would spend every idle moment in the library with Eugene Garfield's enormous ISI citation indexes (especially the Arts & Humanities Citation Index), seeing how other people had responded to articles I was currently reading or had recently read.
Now Google Scholar has enabled citation searching; a search for Nicholson Baker's 1994 New Yorker article Discards, for example, reveals that 53 sources have subsequently cited it (most of them disparagingly, I bet, and unfairly so). Those 53 sources are listed in descending order of their own "Cited by" frequency, with The social life of information by JS Brown and P Duguid at the top of the list, with 2815 citations. To see who in turn cited Brown and Duguid's book, just click on the "Cited by" link, and off you go. This is a fascinating new feature at Google Scholar, and you should set aside some time for it.