I'm not a big believer in Web 2.0. Your opinion may differ, but the word "Web" is a fancy catch-all phrase for the Hypertext Transfer Protocol (HTTP, the protocol used for transferring information between a Web server and your Web browser) and the Hypertext Markup Language (HTML, the markup language that tells your browser how to display whatever text, graphics, etc is coming through the HTTP "pipe"). Over at the World Wide Web Consortium (W3C), there actually are versions of these protocols. HTTP for example is still on version 1.1 and has been since 1999. The most recent of HTML (version 4.01) is just as old. There is something over at the W3C in draft mode called XHTML which is now at version 2.0 and has relevance to the future Web. But a one-to-one mapping of it directly to Web 2.0, especially when you consider how many things have been dropped into the Web 2.0 bucket that don't use XHTML, doesn't work either.
So, when people ask me what Web 2.0 is, a lot of times, I say "It's when the back button doesn't work! (something that usually works with Web 1.0... but not always). The other thing I say is that I don't think there's a trade or servicemark on "Web 1.0." But O'Reilly has the service mark on Web 2.0. That's a big difference too.
We're looking for the Top Ten difference's between Web 1.0 and 2.0. If you want to chime in, send an email to me at david DOT berlind AT cnet.com with your one-liner. Once we get all the submissions, we'll consolidate and run a poll to see which should make it into the top 10. Then, we'll figure something out for the winners.