I’m at Mix10 in Las Vegas where Microsoft has been showing off the latest preview of IE9 – you can try it here, provided you have Vista SP2, Windows 2008 or Windows 7.

The two themes are performance, with GPU-accelerated HTML and graphics and a new Javascript engine that compiles code in the background, and standards support. This latter was not a surprise to me, as I’d heard the well-informed Molly Holzschlag praise Microsoft’s commitment to HTML5 at a workshop here on Sunday – see this earlier post.

During the keynote, we saw IE9 playing a video using the HTML 5 video tag – no Flash or Silverlight needed. Microsoft also showed that in this instance IE9 performed better than Chrome thanks to better hardware acceleration. Although one should always mistrust one vendor’s demonstration of another vendor’s product, it should not be surprising that Microsoft is able to deliver a browser that is better optimised for Windows.

Video, hardware accelerated graphics, audio element support, fast JavaScript: there is considerable overlap with the features of the Microsoft Silverlight (and Adobe Flash) plug-ins.

The plug-in approach has advantages. It offers consistency across browsers, and enables rapid evolution without the hassles of standards committees. The multimedia features in Silverlight and Flash are well ahead of those in HTML 5 – Holzschlag nailed this when she described today’s HTML 5 demos as reminiscent of Flash demos a decade ago.

Still, if you can do without the plug-in you end up with cleaner code, removing the awkward transition between what is in HTML and JavaScript, and what is in the plug-in. There is also a better chance that your code will run on Apple’s iPhone and iPad, for example.

The question though: can Microsoft do an equally good job of supporting HTML 5 throughout its platform, as it will do with Silverlight? This is where I’m doubtful. The Visual Studio and Expression tools will continue to drive developers towards Silverlight rather than HTML 5.

It’s notable that shortly after Microsoft’s IE9 demos at Mix, we saw demos of fun technology like code-name Houston, develop databases in the cloud using just your browser and … Silverlight.