As an agency moves into developing a new interactive marketing/advertising campaign or website the term thrown around with reckless abandon is "Web 2.0". To many firms, this simply means the incorporation of AJAX. The presence or absence of AJAX is not the salient distinguishing feature. It's the social networking aspect the site creates amongst its user. This is not a new complaint. Tim O'Reilly, who's smarter than your mom, has lamented this nexus as a requirement for a while now.
And not to be misunderstood, I'm a big proponent of AJAX, I use it in a lot of projects because the project demands it. However, AJAX was the missing piece of the puzzle that allows HTML to behave like Flash. The ability to read data, refresh the display in a light, quick manner without having to reload the entire page has been around since Flash could parse XML files. So, to say that only an AJAX-driven site can be 2.0, is to also have your eyes closed to the available technology.
The point is simply to remember that Web 2.0 is a concept. One that involves people interacting with each other - that have been empowered to engage in the process of transactional conversations with the user base and with the site itself. A hallmark of a 2.0 site is the ability to *give* content to the site. It's about content assemblage and ownership. Google, Flickr, YouTube, WuFoo, etc - they all provide great, free services, but in turn they are all collecting massive amounts of data.
So what does this mean for companies seeking creative services? Forget about the tools - AJAX, Ruby, whatever. Spend more time finding the creative firm that has a history of developing campaigns with effective response rates. They're in a better position to determine what the right tool is to bring the concepts of Web 2.0 to your campaign.
For developers/designers - remember AJAX is only half of the equation. Granted it's the half that is the user experience. However, AJAX can't write or modify data. You're going to need a programming language (at a minimum) to manipulate the XML files. Oh and yeah, while you're at it, remember your application is going to need to do something useful and can't be dog shit ugly. Inserting AJAX doesn't immediately unscrew a horrendously designed site that serves no purpose.
Now go out and build something with AJAX, because it's a hot shit tool.