I've deliberately avoided this thread because I despise the term
Web 2.0 and I've been very pleased to see others mock it.
Things on the Internetssss don't work like software distributions - there are not marked upgrades or changes that make it differ from one day to the next. Whoever came up with that term was very clever, but everyone who has used it after him should be slapped. Present company excluded, of course.
Usually, people are referring to sites which are interactive and allow a certain amount of content control and editing by surfers who have become part of the site's free membership. Commenting, reviewing, content rating/voting, social-networking, and the uploading of content by members are some pretty typical characteristics.
How many adult sites really allow for that type of interaction with their surfers?