Who coined the phrase Web 3.0?

Answer

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 were the ones who thought of this idea.

[edit: actually, the origin of Web 2.0 was a book by one Dermot McCormack, titled Web 2.0: 2003-'08 AC (After Crash) The Resurgence of the Internet & E-Commerce in 2002, three years before O'Reilly supposedly coined the term.]