I was asked this question for a podcast at the recent Under the Radar conference where Zvents presented. You can test my memory by hunting up the actual podcast, but I am pretty sure this is the same answer I gave:
It means two things -- one technological, and one social.
Socially, it's the return of hope and enthusiasm to Silicon Valley. People may mock "bubble 2.0" and naysayers can always point to some particular point of excess, but the reason we entrepreneurs are here is to change the world, and a lot of dreams lay dormant from 2001 to 2005. Those dreams are being knit into reality today, and many of us can see that we'll be able to make the world a very different, and hopefully better place, soon.
Technologically, it's about data as a platform (just like Tim O'Reilly said) and more importantly, it's about fast and simple integration of that data. Mashups may occasionally be dorky, but they demonstrate a level of interoperability that is simply astonishing when compared to 1999. We've all seen network effects accelerate change and growth to warp speed -- what we're seeing now is kind of Metcalfe's Law of web functionality, where the value of every interoperable web service is the square of the number of other services to which it can be connected.
Hmmm. I know I didn't say that one in the podcast. It may actually be worth its own post.
But, back to work. Big customer meeting tomorrow...
...Web 2.0 means the return of customers. Yee Hah!