Look no further than Windows Live Mail for Web 2.0
I figure that Windows Live Mail is a good example of Web 2.0! Live Mail behaves like a local program even though it is a webpage! This is particularly evident in the lack of general page refreshing that was found in the original version of Hotmail! Therefore I believe that 2.0 describes a persons program usage experience....and to be Web 2.0 there should be no overall page refreshing, the webpage / website should behave like a locally installed program!