Aral made an interesting point a few days back on AJAX and the browser as a plugin. I thought I'd pick up on that as its something I've been thinking about for a while now. In many ways computers these days are not stand-alone machines, connectivity has become an integral part in all aspects of computing. Whereas in the past there was a very clear distinction between the web and the desktop, you increasingly see those two worlds overlapping. The very first signs of this started to come up some years ago when businesses started using activeX components etc. for enabling their online application to interface with the client's computer. The second phase is increasingly prevalent with desktop applications connecting up to the web to exchange data and make it available for offline use. What I expect to see happening in the not too distant future is the ability to move beyond the limitations of the browser or desktop application shell.
If you think about this what immediately comes to mind is 'widgets' but its so much more than that. Right now we've come to the point where data has escaped from the clutches of the implementation dictatorship, meaning you can use it just about anywhere you want - be it the web, a desktop application or a mixture of the two - no matter where that data is located. But what about the application itself? There things get a bit trickier, you immediately deal with implementation constraints. Does your application run on the server or as a desktop application? That is one example of an implementation constraint you need to take into account the moment you start developing.
Now, if you think about that - why should it matter? It is commonly accepted that data is simply data, the same ubiquity should apply to an application wherever you run it. Whether you navigate to an MXML document using your browser, launch it as a standalone widget or embed it in a desktop application it should not matter.
We're steadily moving towards applications as services, running self-contained or seemlessly embedded in any other technology. This is a huge paradigm shift but no doubt a very necessary one.