Web 1.0 = set of Web technologies (like HTML, JavaScript, HTTP, …)
Web 2.0 = new name for applications that use Web 1.0 technologies in a novel ways
Web 2.0 application usually offers open XML based interface
rich user interface (utilizing AJAX)
Web 3.0 = the future vision of semantically rich Web
some day missing XML features will be implemented
you can prepare for this moment right now
store your content in a semantically rich XML
convert it into dumb HTML on the server today
send it as XML when Web 3.0 is ready