As the term Web 2.0 continues to spread rapidly some people still think it's all about shiny cute mirrored graphics used nowadays but to correct this we should also tell that Ajax is also involved along with the new theme of sites of social bookmarking (digg.com and delicious.com) What's your definition of Web 2.0 ? Do you like it ? Do you think normal visitors (not webmasters) noticed the difference ?
I think it involves more use of AJAX, like vBulletin forums have AJAX controls for replying to posts, using thread tools, etc.
It can all be summarized in increased interactivity and seamlessness of jumping from one point to another, all under the veil of social networking.
I think of web 2.0 as something userpowered/social, free, something with tabbed navigation, ajax, large fonts, beta, over-sized elements like search boxes, something accessible and quick loading, bright, stylish and glossy.