On the browser front, the big news was the early preview of IE9. For web enthusiasts, it's fun to wax poetic about the mind blowing speed of V8 or the brilliance of TraceMonkey, but these technologies will always be secondary at best. If you are a web developer the most important browsers are the ones from Microsoft, because they dominate the market. They form the baseline that you develop against. If you want to do something that these browser do not support, you have got to get creative or be willing to live with your work simply being a toy. Simply put, IE9 news is more important than all of the Firefox, Safari, Chrome, and Opera news combined.
Luckily, Microsoft did not disappoint with IE9. It is obviously a far from finished product, and Microsoft was a little too dodgy on sharing its roadmap for my taste, but I can empathize with their position. Still they showed a browser with significant speed improvements and with support for a lot of standards based, visual eye candy. I'm talking about a lot of CSS3 features and most surprisingly, an amazing SVG implementation. They whipped out some classic Microsoft tricks, i.e. using their intimate relationship with their operating system to tap into GPU acceleration. You might think it's not a fair trick for them to do, but who cares? The boys at Mozilla, Apple, and Google have to accept this challenge, even if it will be super painful to pull of across platforms -- and Linux will surely suffer here once again.
Of course that definitely does not mean that these features are out of IE9. I think there is a lot more to come. Microsoft has done some amazing work to give IE9 a lot of graphics features, but they have left out Canvas. Further intense graphics programming would benefit from the multi-threaded programming model supplied by Web Workers. So it would make a lot of sense for both of these to be added. I'm even optimistic that Microsoft will implement these standards directly, and not offer some proprietary alternative.
All of this makes you wonder about IE9 as a compelling graphics/gaming platform. I think that some serious tooling will be needed to make this viable. That's an area that Microsoft excels at. However, would this not put Microsoft in conflict with their own efforts around Silverlight? It's like the HTML 5 vs. Flash war could be played out in miniature within Microsoft's walls, only it would be IE9 vs. Silveright. Speaking of Silverlight...
The other big news, from my perspective at least, that came out of MIX was a lot more information about the Windows Phone platform. As a mobile developer, I have very mixed feelings about Windows Phone. On one hand, I really like the idea of using Silverlight as the application platform. This is a mature application platform, with fantastic tooling. You get to use a beautiful programming language -- C# (oh an maybe other .NET langs, like F#?) that has a decent runtime that includes garbage collection. However, Microsoft looks like they are copying Apple's approach. A lot of the restrictions being placed on non-Microsoft applications are very similar to the restrictions placed on iPhone applications.
Back to the browsers... Microsoft shipped a preview of tools for building Windows Phone applications. Again, major props to Microsoft for getting this software ready out at MIX, even if it is a little rough in places. I don't like companies using end users as a substitute for QA, but this is different. Getting tools into the hands of developers is critical. In this case, the tools include a Windows Phone emulator, which includes *drumroll please* the Windows Phone browser! As a mobile developer, this is the most important thing that can be included. I'll have to support your browser before I have to support your application platform.
However, the Windows Phone browser is not very promising. It seems to be based on IE7. It does not seem to support many HTML 5 features at all. No geolocation. No local storage. No application cache. No web workers.
Maybe some of these things will be added by this fall, but I'm not as optimistic about this. Even the documentation that is included emphasizes building web applications that are designed to work on legacy browsers. They seem to be saying, don't go looking for coolness in the browser!