Web technologies had matured from α-stage to β-stage, in the early years, and then progressed through versions 1.0, 1.5, and finally have reached the Web 2.0, we know and use today. Many suggest that Web 3.0 is also a legitimate version that we are entering into. The general consensus is that the semantic web is Web 3.0
Web 1.0 – The first incarnation of the web was akin to dancing bears: it is not how well they dance, but the fact that they can dance is novel enough. This version of the web, dubbed Web 1.0 after the fact, involved mostly static brochureware types of applications, which were very useful by themselves. There were few dynamic capabilities, very little context, and almost no interactivity. Moreover, the websites did not leverage the intelligence inferences from the user interactions.
Web 1.5 – Then came the Web 1.5 era of electronic commerce, with sites such as eBay and the first generation of Amazon. One could not only buy books, toys, and a whole host of other things online, but also auction any surplus.
Web 2.0 – Now the bears can waltz, or the other way around: If the bears are not waltzing, the users are not interested anymore. We need the ability to search, we need intelligent conclusions, we need interactivity, we need speed, we need rich multimedia; all characteristics of Web 2.0. Now we not only want to buy stuff, but also to read all the 1-star reviews as well as see what others who bought similar items also purchased. We want to keep a wish list, we want to set up and manage invite lists electronically, we want to meet folks who will be at the city we visit, we want to share our photos, our thoughts, our ideas, we want to have political debates, we want to keep a list of movies to watch, we want to communicate with companies about what they should make—and all online, of course. This is where the web is now; this is Web 2.0. And notice that although none of this is defined by any particular technology, a host of technologies are behind it.

A good depiction of the growth of the Internet is shown in the website http://crave.cnet.co.uk/software/the-50-most-significant-moments-of-internet-history-49299033/

Web 3.0 – Technology is not static; neither is social and business progress. Web 3.0 is the next frontier that holds the age of intelligent information and the semantic web. In Web 2.0, context and meaning are still externalized in programs, servers, and protocols; the data still is pretty much anemic in terms of meaning. In the case of Web 3.0, when powered by semantic web technologies; the data will be annotated with meaning, context, and most important, the relationship with other data.

If you ask 10 people what the basic characteristics of Web 2.0 are, most probably you will get more than 10 different answers. Eric Schmidt, CEO of Google, has a very interesting answer to the “What is Web 2.0” question, which is of course captured at this video