Web 2.0

Web 2.0 is a term coined by Dale Dougherty, along with Corkman Tim O'Reilly, who is one of the cofounders of O'Reilly Media (a big publisher) and a great supporter of both free software and something called the open source movement. Open source means that the computer code that makes up a piece of software is available to the public, which is invited to improve and to change the software. Where Web 1.0 means companies and professionals putting web pages and content out there, and consumers just consume, Web 2.0 can be thought of as both reading and writing to the Web - for everyone! It is all about communities, sharing, Wikis and blogging. It's about tags, metadata (data about data), Flickr, MySpace and RSS. In an nutshell, it's all about collaboration and interaction, creating instead of consuming, social networks, business networks, communities of practice, citizen journalists and user generated content. It's back to its true roots, the way it was first envisioned. Communities and their user generated content have now become commodities, with community sites like MySpace and YouTube being sold for vast amounts of money .There is a drive in humans to build and to be creative, and Web 2.0 enables them to do this. It has become the new social phenomenon where thoughts, community and experience have become explicit and a valuable commodity

Web 3.0 or a "Semantic Web"

Web 3.0 is the next step in Web evolution. We aren't really there yet, but it's the term that's being currently used to describe the next generation Internet, and it's also called the "Semantic Web" (and again Sir Tim Berners-Lee is behind a lot of this). While Web 1.0 was static and more for looking than creating, and Web 2.0 all about community and interaction, well, Web 3.0 is about the data. The aim of the Semantic Web is to make the data that's available on the Web machine-understandable. This will happen by adding metadata (data about data - think of the labels you get on the side of a packet of cereal, giving you more information about it) to the Web, this way helping your computer to "understand" what the data is all about, helping you to find it quicker and make more of it.
Computers are quite literally dumb - they don't understand what data is, or what the information means in a Web page. It is the human being that is needed to understand the Web page, to get the meaning (the "semantics") of what they are reading. Computer scientists and organisations like the W3C are working on this concept of a Semantic Web by developing new languages to help put this metadata in place on our Web pages and into literally all the data that's available on the Web. It is well underway at the moment and new languages called RDF and OWL have been developed. It's not quite Artificial Intelligence, but the human intervening to make the Web become a smarter Web, a new improved Semantic Web by putting a new layer of technology over the existing layer that exists there already today.
However, you are probably thinking, "How on earth will they achieve that? There are billions of Web pages already!" This is one of the great difficulties: to make the Web a more efficient place, to organise data, to add all this metadata to the Web pages. It is a massive project and will require a lot of effort. However, making the Web smarter by adding this machine-understandable layer will help in the long run to make us more productive and efficient. Think of it as the Web going from a massive disorganised library to a highly organised one. With bazillions of Web pages being produced it's also difficult to sift through them all to find precisely what you need, and the Semantic Web aims to improve searching for data, too. When the Web 3.0 - the Semantic Web - comes about, machines will take a lot of the workload from humans and help them with a lot of repetitive tasks. It's in the very early stages and there are no buttons to press to make the Semantic Web instantaneously appear. It will take time and a number of applications will gradually emerge along the way as it progresses.
If you want to understand a little bit more about the Semantic Web and what it is, have a look at this video on YouTube (search for "Semantic Web"): http://www.youtube.com/watch?v=sepq4m0oAY8 . Eyal Oren of DERI (Digital Enterprise Research Institute) here in Galway does a good job explaining it!

Web 4.0

With Web 3.0 in full swing behind the scenes, Web 4.0 is underway! Web 4.0 is when all the technologies come together and the Web gets incredibly smart and efficient and begins to head into the area of Artificial Intelligence. It's a Web in the future where the Web itself becomes intelligent. It's the next stage of web evolution perhaps 20 or so years down the road....