On ZDNet I've written an article outlining some common elements of a modern website or app.
A lot of the features and functionality of so-called Web 2.0 sites are now common elements in most current web apps and sites. It's really gone beyond what was labelled 'Web 2.0' last year, because so many mainstream websites are now using these elements. It's no longer a niche trend. For your reference here is a summary of some of the popular elements in use by modern web sites and services [...]