What is Web 2.0

Web 2.0 is Social interaction and collaboration  on the web.  Kind of a spinoff of Facebook and MySpace, Web 2.0 sites usually focus on a particular genre, like ebay, craigslist, etc.  Used mostly in  focus groups, networking, charity fundraising, or, most recently with the Barack Obama presidential campaign.

I am not sure what enterprise 2 is, but I suspect it would be part of the web 2.0 umbrella. Just a hunch. Not necessarily something that would need to be differentiated I would think.

Web 2.0 is all about social interactions.  Great examples include Richard Rosenblatt's Demand media.  They are socializing websites and web based applications.

I believe enterprise 2.0 is the term applied to how the next generation of enterprise applications will be enhanced on the web.  Look to Google & Salesforce.com integrating for that, I bet.