SWYL: What is Web 2.0?

There has been a lot of buzz going on in the internet space, especially with Web 2.0 and the like. Recently, a friend of mine (who works for a big IT company) happened to ask me a question regarding Web 2.0 and SOA. He asked me-

Is Web 2.0 different from SOA? I've been reading about Ajax and so many other Web 2.0 stuff, but how does SOA fit here?

I did take him through a 15minute session to answer his question (hope it was useful!) But then, I thought of putting down my thoughts in the areas of Web 2.0 and SOA as a part of my SWYL articles. So, in this article I thought of touching upon Web 2.0. I know that Tim O'Reilly has the best explanation for this. An excerpt from O'Reilly goes this way-

The concept of "Web 2.0" began with a conference brainstorming session between O'Reilly and MediaLive International. Dale Dougherty, web pioneer and O'Reilly VP, noted that far from having "crashed", the web was more important than ever, with exciting new applications and sites popping up with surprising regularity. What's more, the companies that had survived the collapse seemed to have some things in common. Could it be that the dot-com collapse marked some kind of turning point for the web, such that a call to action such as "Web 2.0" might make sense? We agreed that it did, and so the Web 2.0 Conference was born.

For a detailed view, you can see the article at O'Reilly.

I however like the following way Web 2.0 was differentiated from Web 1.0 at O'Reilly-

Web 1.0 --> Web 2.0
DoubleClick --> Google AdSense
Ofoto --> Flickr
Akamai --> BitTorrent
mp3.com --> Napster
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
publishing --> participation
content management systems --> wikis
directories (taxonomy) --> tagging ("folksonomy")
stickiness --> syndication