Thinking about the state of Web Development, two things come to mind. The first is positive, that people are doing really awesome things with limited resources providing users with mind-boggling, plugin-free rich experiences that are platform independent. The second thing is less positive, and that is a set of broken languages and standards that make for varying experiences on different browsers.
So I am starting to think, and I'm not convinced yet, that it may not make sense to build a single application to serve all browsers. Here's my reasoning:
Where the business and architectural logic is at fault is that since the AJAX craze, people have forgotten about Flash for building rich web applications. Sometimes Flash makes sense, in that download sizes for code are way smaller and performance is way better. Sites like netvibes almost certainly would have better performance and capabilities if they were developed in Flash using Flash Remoting. Flex also has its places, although I think the XML as everything approach to scripting languages is getting a little ridiculous. XML is fine for data, but when you need to define logic, XML is a little bulky at best.
Still, even with the above happening, I think that the future will be where we have been in the past. Detecting a browser and through various means, serving the appropriate application for a specific browser. Web teams are going to get bigger, because the future isn't in OSs or desktop applications, it is on the web.