Web 2.0 is a term that's getting more and more attention these days. Not only positive press by the fawning sheep who think they've personally discovered something amazing and need to bring it to the unwashed, but a lot of negative commentary as well. 

What is Web 2.0? Well it depends on who you talk to - it could be service oriented web technologies (if NTP ran on HTTP, we could call it Web 2.0 pre-1985), community collaboration (e.g. Wikis like wikipedia, group tagging like flickr, etc), or a richer environment courtesy of the more prevalent use of more advanced technologies (like, cough, AJAX - some people, hanging onto Google Suggest's coattails, decided that it was important that they declare a terminology for this "new" technology that had actually been in use for over half a decade).

That last point deserves a bit of attention - why is it that recently some great web applications like Google Maps and Flickr have appeared, offering so much more usability than their predecessors? What technological revolution occurred to make this happen? Did AJAX just get discovered by some researchers who found some magical new way of making browsers sing?

...we've had the so-called AJAX for years, and it has been in use by intranet web teams since the late-90s/early-00s...

The answer, of course, is that we've had the so-called AJAX for years, and it has been in use by intranet web teams since the late-90s/early-00s. It was, however, primarily the domain of teams that could mandate that their userbase would use Internet Explorer, as that browser was the leader (by far - you don't have to love Microsoft to acknowledge this reality) as an interactive web application platform. I had the luxury of making such a declaration, and was developing monitoring and control web applications that used XML data islands, msxml's XMLHttpRequest, client side XML transformations on demand with changing parameters based upon user input, layered transparent graphics for usability, and so on: In real-time you could monitor the status of tens of giant power generators across the continent, and with a click of a button - well along with a confirmation - you could control them. This was about 5 or 6 years ago. I was hardly unique - in fact I've never even considered myself a web developer, and this was just a one-off style solution where the web interface was the best choice, so I took a breather from back-end/database development to build this solution.

So why didn't the technology take off on mainstream websites? One simple reason - Netscape 4.x. Quite a few corporations stuck with their decision to back Netscape in the browser wars - which they backed largely for its theoretical cross-platform advantages - even after Netscape was terribly obsolete and basically dead (for example I did some work for Bell Canada a couple of years ago, and the desktop standard throughout the entire organization was Netscape 4.x. Of course many users figured out where to find the hidden iexplore.exe icon and covertly used it instead). If you made a public website where you couldn't reasonably mandate a particular browser, you developed for the lowest common denominator, and that denominator was Netscape 4.x (even if you had 0 visitors using that browser, it was just good practice to avoid tying to Microsoft's software, so you targeted the cross-platform leader. That leader was Netscape).

Now, of course, the big competitor is Mozilla cum Firefox. Featuring modern DHTML capabilities, XMLHttpRequest functionality, and most of the other major web app functions, and offering full cross-platform functionality, Mozilla completely changed the landscape. Suddenly the "lowest common accessible denominator" was pretty powerful, so there is no reason to hold back empowering your site.