I've copied and pasted this off wikipedia: 'The term "Web 2.0" is commonly associated with web applications that facilitate interactive information sharing, interoperability, user-centered design, and collaboration on the World Wide Web. A Web 2.0 site gives its users the free choice to interact or collaborate with each other in a social media dialogue as creators of user-generated content in a virtual community, in contrast to websites where users are limited to the passive viewing of content that was created for them.'
Examples of Web 2.0 include social-networking sites, blogs, wikis, video-sharing sites, hosted services, and web applications.
So, guess what? Technically, this TEFL.NET (and this forum) is web 2.0!
How many Web 2.0 tools have I used whilst teaching? Very few! --one reason being that I tend to design my own tools and set them up locally on networked computers in the classroom when possible, if I decide I want IT to assist the lesson. For example, a slide show in Powerpoint where I've chosen the pictures and the learners (in groups of 2 or 3, etc.) are free to interpret them and develop a story (changing the order, too, if they like). The results are quite funny! But, www.mes-english.com
has a good crossword generator. Users just type in the clues and the answers (...careful --sometimes their pictures don't match the clues...but fortunately the pictures are an option).
I think, fundamentally, what's being inferred as important in the use of Web 2.0 tools that you're hearing is the "information sharing" and "collaboration" part which naturally gives learners a sense of empowerment and gets them contributing to how the class as a group is being taught.