I am encouraged by your feedback.  Let me clear it up a bit first: my version is written basically with Paul Graham's article on this topic in my mind.  I think that article is neither an undue appraisal nor an unfair dismissal of the term, and I think it would be a good and neutral starting point for me when I re-write the lead.
 According to that article, Web 2.0 can be boiled down into three things: democracy, Ajax, and focus on user.  This is how I structure the lead sentence: democracy (ie architecture of participation in Tim O'Reilly's words, and folksonomy in realisation) and user focus in the first part, and better UI powered with Ajax in the second.
 Specific replies as follows:
 lengthy list: agree, although the current version also features a long list as well.  Perhaps we can break down that clause into two, like this:
 ... that put emphasis on allowing users to share and collaborate information online in new ways as part of the service, presented in a user-friendly, interactive, and often Ajax-enabled, user interface.
 "collaborate information": my wrong.  Let's preserve the order in the current version, ie "collaborate and share information".
 folksonomy: see my point re: democracy and architecture of participation above.  I do believe that this is an important feature that distinguish Web 2.0 from the old: a platform, built-in as part of the service, that allows users to actively contribute to the grouping and ranking of contents.  You won't have that pre-Web 2.0.  Even the readers' ranking at Amazon.com was initially a secondary feature.
 cluttering the lead: please see if the revised version above would make it better presented.  And as I have mentioned above, the original version suffers from the same problem as well.
 focus on what web 2.0 is: I believe this is what I am doing with the revised version.  The current version simply mentions too much of O'Reilly Media, but the term has evolved far beyond their reach and control.  And I do believe the revised version does sufficiently address the fact that it has become a buzzword in the marketing sense.