According to Tim O'Reilly Web 2.0 is not yet clearly defined but he listed some transitions from Web 1.0 to Web 2.0, as follows:
|Web 1.0 -->||Web 2.0|
|DoubleClick -->||Google AdSense|
|Britannica Online -->||Wikipedia|
|personal websites -->||blogging|
|evite -->||upcoming.org and EVDB|
|domain name speculation -->||search engine optimization|
|page views -->||cost per click|
|screen scraping -->||web services|
|content management systems -->||wikis|
|directories (taxonomy) -->||tagging ("folksonomy")|
BitTorrent thus demonstrates a key Web 2.0 principle: the service automatically gets better the more people use it.
Wikipedia is already in the top 100 websites, and many think it will be in the top ten before long.
There are more than 100,000 open source software projects listed on SourceForge.net.
One of the most highly touted features of the Web 2.0 era is the rise of blogging.
Writely is a new site that allows collaboration between Internet users (this site was bought out by Google in 2006).
Ajax is a website that allows personal computer applications.