Being a web developer (not a designer, thankfully) it’s a lot easier to differentiate Web 1.x versus Web 2.0 sites. That’s mainly due to the fact that I live "behind" what the user sees, whereas a designer defines what the user sees and how the user experiences the site (UI/UX).
That said, designers have the harder line to toe, that Web 2.0 is NOT a design aesthetic, it’s not about diagonal lines, reflections, large call-to-action ribbons, gradients, bevels, and high-contrast color schemes.
Then again, designers must know the difference between web 2.0 and design aesthetic. Moreover, they must feel passionate about their design and that have enough (how do I say this without offending my friends in the design world?) "wherewithal" to stand up for their convictions (even if it means losing the bid, or offending the client) that
"Web 2.0 refers to a perceived second generation of web-based communities and hosted services which aim to facilitate collaboration and sharing between users.
"Although the term suggests a new version of the World Wide Web, it does not refer to an update to any technical specifications, but to changes in the ways software developers and end-users use the internet." (http://en.wikipedia.org/wiki/Web_2)
Did you see where it mentioned "design" in the definition of what Web 2.0 is? No? That’s because it’s not there. Which brings us full-circle:
– is a concept
– is not a design aesthetic