Web 2.0 has been with us for a while, but the exact definition of what Web 2.0 means is still controversial. No matter which definition you prefer - Tim O'Reilly's, Wikipedia's, Paul Graham's, or the famous Web 2.0 validator's – it's clear that some companies do it better than others. In fact, you could argue that some companies have been doing it before the term was coined.
So, in your opinion, which company – recent or old [in internet years] sets the best example of Web 2.0?