Web 2.0 websites typically include some of the following features/techniques. Andrew McAfee used the acronym SLATES to refer to them:
The ease of finding information through keyword search.
Ad-hoc guides to other relevant information.
The ability to create constantly updating content over a platform that is shifted from being the creation of a few to being constantly updated, interlinked work. In wikis, the content is iterative in the sense that users undo and redo each other's work. In blogs, content is cumulative in that posts and comments of individuals are accumulated over time.
Categorization of content by creating tags: simple, one-word user-determined descriptions to facilitate searching and avoid rigid, pre-made categories.
Powerful algorithms that leverage the Web as an application platform as well as a document server.
The use of RSS technology to rapidly notify users of content changes.
Other than the extensions, PM has all of the above, and has done for a long time.