Interesting Web 2.0 explanation article .

Rusty, I believe that you are confusing Internet 2 with Web 2.0.

I think that Web 2.0 is actually more of a business definition than anything else.

Friendly sites that are content or function centric, and leverage new technologies (regardless of what they actually are) to deliver lightning fast and highly intuitive user interfaces would generally be considered Web 2.0.

From a design perspective, they tend to have larger fonts, highly clean visual styles, bright friendly colors and minimal clutter. Users are presented with a minimum number of choices on any given page, and graphical buttons, and highlighted boxes are used fairly liberally to make it very obvious to a user what they need to do.

From a technical perspective, these sites tend to look like this: Database -> Web Server -> Client Side Web Application -> End User Page. It is the addition of the "Client Side Web Application" that really sets most Web 2.0 Design aside, technically. The old model (and the model that Joomla! sites still tend to use, for the most part) is that a user gets a page, does something and then clicks a submit button, and waits for another page to load.

Web 2.0 sites load a "stub" application, which then communicates back and forth with the server in the background, and, instead of reloading a page, overwrites the pages DOM (Document Object Model) to change the information there. This makes Web apps feel more like "normal" computer programs, and less like Web pages. This technical wizardry is often accomplished using something called AJAX, which stands for "Asynchronous JavaScript and XML". So, even when people talk about AJAX, it is sometimes hard to know exactly what they are talking about, because there are loads of AJAX frameworks out there, and nothing stopping anyone from implementing their own as well.

It should be pretty evident that ANY of the major web scripting languages (PHP, ASP, Cold Fusion, etc.) could be used to implement an AJAX type Web app. It would even be possible to write such an app that used pure HTML for the base pages, and communicated more or less directly with a database -> XML service, although I can't think of many reasons why that would be desirable.

Back to my original point, however, since the definition is more of a business one than a technical one, any of those rules can, and are, broken on any number of sites that are still rightly considered Web 2.0 sites.

PHP, with its extremely wide array of open source code bases, easy interoperability with virtually every database known to man, and very well developed AJAX libraries is certain to be a mainstay of Web 2.0 development for a long time to come.

FWIW, AJAX has a bit of a limitation (although it can be gotten around with a bit of effort) in that it is largely restricted to pulling resources from a specific domain, instead of cross-domain pulling. There are a lot of good "mashup" sites out there that riff off of Google Maps, for instance, but combine them with other databases (SF BART schedules, for instance) to produce really neat hybrid Web apps. As this sort of thing matures, expect to see a lot more of this sort of thing, mixing and matching information from multiple sources all at the same time. Of course, a whole rash of legal actions will follow these sites as well.