Better interface design is at the core of Web 2.0, one might reason, so I am in full agreement that the advances in the visual environment that have been speared on by usability and functionality concerns ought be included as part of the overall development curve, and be associated with the version in which they are introduced.

All of the visual trappings in KW's web 2.0 design list, posted above by kgun, have been around long before Web 2.0, but the trend toward their practical use in meaningful, associative and interactive ways has taken on steam within this part of the curve. It is as much Web 2.0 as any AJAX script.