Tim O'Reilly, the reputed "father" of the term web 2.0, writes an informative article on what web 2.0 is (though if you seek out an impromptu interview thats on utube asking him what it is - he cant answer ). This article has some comparative examples of old style "web1.0" vs Web 2.0 - it also has some nice key elements listed throughout of web 2.0
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