The web as is stands (Web1.0) is seen as a "static" thing, like a billboard or a magazine. You can see lots of billboards, buy lots of magazines, enjoy or dislike them but they stay the same until they are changed by the publisher.

"Web2.0 applications" are ones that are "user-generated" or "user-shaped". Instead of being "published" by someone, the people using the site "publish" the content. They also market it and edit it.

Famous examples of "Web2.0 applications" already in use and much talked about are Flickr for photographs, Wikipedia for encyclopedia articles, Facebook for maintaining friendships, YouTube for seeing young people mugging to videocameras and Answers.com for combining syndicated elements of these with its own user-generated Q&A section.
Web 1.0 is like a kind of platform where there are new releases of it. But there is nothing like a new release for the existing ones in web 2.0. Web 2.0 is a kind of service oriented. Web 1.0 was about publishing, not participation; that advertisers, not consumers, ought to call the shots; that size mattered, and that the internet was increasingly being dominated by the top websites. Web 2.0 helps to increase the participation of the users like blogs, e-commerce websites, torrents etc, where every user gets a chance to publish in a website one way or the other.

For Ex: Napster (though shut down for legal reasons) built its network not by building a centralized song database, but by architecting a system in such a way that every downloader also became a server, and thus grew the network.