"Web 2.0" is an example of what the historian Daniel Boorstin would have called "the Fertile Verge" - "a place of encounter between something and something else." Boorstin (and here I am wholly indebted to Virginia Postrel) pinpointed such "verges" as being nothing short of the secret to American creativity.
Postrel sums up what Boorstin was saying as follows:
"A verge is not a sharp border but a frontier region: where the forest meets the prairie or the mountains meet the flatlands, where ecosystems or ideas mingle. Verges between land and sea, between civilization and wilderness, between black and white, between immigrants and natives...between state and national governments, between city and countryside - all mark the American experience."
The creativity of America, Boortsin argued - the hope of the nation - lies "in its verges, in its new mixtures and new confusions."
My point is that there is no boundary between "Web 1.0" and "Web 2.0" - just a blurry verge. And the richness of the verge lies in the cross-fertilization and new combinations they encourage.
This notion of the verge or the liminal is very popular with postmodernists. (I'm surprised Wikipedia doesn't refer to the postmodernist usage.) But my favorite observation regarding the fertility of the verge or the liminal is this one by Norbert Wiener in the introduction to his book Cybernetics:
There are fields of scientific work, as we shall see in the body of this book, which have been explored from the different sides of pure mathematics, statistics, electircal engineering, and neurophysiology; in which every single notion receives a separate name from each group, and in which important work has been triplicated or quadruplicated, while still other important work is delayed by the unavailability in one field of results that may have already become classical in the next field. It is these boundary regions of science which offer the richest opportunities to the qualified investigator. They are at the same time the most refractory to the accepted techniques of mass attack and the division of labor. [emphasis added]
I think Wiener's observation is particularly apropos in the context of Web 2.0: much of the confusion is caused by the fact that "every single notion receives a separate name from each group".